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 $154.41   11.669%   $172.4281   $172.43   $172.45   $172.40  
  Purchase #2 $58.79   11.663%   $65.6467   $65.65   $65.65   $65.60  
  Purchase #3 $238.57   6.290%   $253.5761   $253.58   $253.60   $253.60  
  Purchase #4 $28.84   11.770%   $32.2345   $32.23   $32.25   $32.20  
  Purchase #5 $115.33   4.570%   $120.6006   $120.60   $120.60   $120.60  
  Purchase #6 $201.65   11.389%   $224.6159   $224.62   $224.60   $224.60  
  Purchase #7 $71.99   4.459%   $75.2   $75.20   $75.20   $75.20  
  7 purchase totals = $869.58       $944.3019   $944.31   $944.35   $944.20