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 $48.60   10.313%   $53.6121   $53.61   $53.60   $53.60  
  Purchase #2 $138.39   5.687%   $146.2602   $146.26   $146.25   $146.30  
  Purchase #3 $132.94   11.184%   $147.808   $147.81   $147.80   $147.80  
  Purchase #4 $139.52   9.389%   $152.6195   $152.62   $152.60   $152.60  
  Purchase #5 $123.59   6.793%   $131.9855   $131.99   $132.00   $132.00  
  Purchase #6 $198.34   7.569%   $213.3524   $213.35   $213.35   $213.40  
  Purchase #7 $21.99   6.490%   $23.4172   $23.42   $23.40   $23.40  
  7 purchase totals = $803.37       $869.0549   $869.06   $869.00   $869.10