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 $146.95   7.103%   $157.3879   $157.39   $157.40   $157.40  
  Purchase #2 $208.67   8.384%   $226.1649   $226.16   $226.15   $226.20  
  Purchase #3 $22.82   13.370%   $25.871   $25.87   $25.85   $25.90  
  Purchase #4 $95.89   9.229%   $104.7397   $104.74   $104.75   $104.70  
  Purchase #5 $44.45   8.277%   $48.1291   $48.13   $48.15   $48.10  
  Purchase #6 $213.52   10.713%   $236.3944   $236.39   $236.40   $236.40  
  Purchase #7 $222.78   6.415%   $237.0713   $237.07   $237.05   $237.10  
  7 purchase totals = $955.08       $1,035.7583   $1,035.75   $1,035.75   $1,035.80