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 $229.47   13.392%   $260.2006   $260.20   $260.20   $260.20  
  Purchase #2 $212.46   6.206%   $225.6453   $225.65   $225.65   $225.60  
  Purchase #3 $104.90   8.476%   $113.7913   $113.79   $113.80   $113.80  
  Purchase #4 $207.64   10.430%   $229.2969   $229.30   $229.30   $229.30  
  Purchase #5 $152.98   10.393%   $168.8792   $168.88   $168.90   $168.90  
  Purchase #6 $209.85   7.869%   $226.3631   $226.36   $226.35   $226.40  
  Purchase #7 $170.55   5.263%   $179.526   $179.53   $179.55   $179.50  
  7 purchase totals = $1,287.85       $1,403.7024   $1,403.71   $1,403.75   $1,403.70