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 $102.31   9.428%   $111.9558   $111.96   $111.95   $112.00  
  Purchase #2 $48.48   4.102%   $50.4686   $50.47   $50.45   $50.50  
  Purchase #3 $25.46   11.412%   $28.3655   $28.37   $28.35   $28.40  
  Purchase #4 $62.67   3.405%   $64.8039   $64.80   $64.80   $64.80  
  Purchase #5 $13.58   9.354%   $14.8503   $14.85   $14.85   $14.90  
  Purchase #6 $77.65   11.465%   $86.5526   $86.55   $86.55   $86.60  
  Purchase #7 $60.43   3.730%   $62.684   $62.68   $62.70   $62.70  
  7 purchase totals = $390.58       $419.6807   $419.68   $419.65   $419.90