Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $243.62   13.273%   $275.9557   $275.96   $275.95   $276.00  
  Purchase #2 $152.79   10.325%   $168.5656   $168.57   $168.55   $168.60  
  Purchase #3 $105.89   8.684%   $115.0855   $115.09   $115.10   $115.10  
  Purchase #4 $211.45   13.409%   $239.8033   $239.80   $239.80   $239.80  
  Purchase #5 $238.40   13.764%   $271.2134   $271.21   $271.20   $271.20  
  Purchase #6 $229.72   13.354%   $260.3968   $260.40   $260.40   $260.40  
  Purchase #7 $155.37   8.494%   $168.5671   $168.57   $168.55   $168.60  
  7 purchase totals = $1,337.24       $1,499.5874   $1,499.60   $1,499.55   $1,499.70