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 $10.31   7.571%   $11.0906   $11.09   $11.10   $11.10  
  Purchase #2 $236.95   9.304%   $258.9958   $259.00   $259.00   $259.00  
  Purchase #3 $86.48   12.765%   $97.5192   $97.52   $97.50   $97.50  
  Purchase #4 $41.41   7.747%   $44.618   $44.62   $44.60   $44.60  
  Purchase #5 $247.29   13.807%   $281.4333   $281.43   $281.45   $281.40  
  Purchase #6 $226.90   5.502%   $239.384   $239.38   $239.40   $239.40  
  Purchase #7 $126.68   9.726%   $139.0009   $139.00   $139.00   $139.00  
  7 purchase totals = $976.02       $1,072.0418   $1,072.04   $1,072.05   $1,072.00