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 $217.65   6.657%   $232.139   $232.14   $232.15   $232.10  
  Purchase #2 $89.73   13.596%   $101.9297   $101.93   $101.95   $101.90  
  Purchase #3 $96.46   12.237%   $108.2638   $108.26   $108.25   $108.30  
  Purchase #4 $129.97   4.170%   $135.3897   $135.39   $135.40   $135.40  
  Purchase #5 $151.88   11.528%   $169.3887   $169.39   $169.40   $169.40  
  Purchase #6 $201.76   5.396%   $212.647   $212.65   $212.65   $212.60  
  Purchase #7 $60.37   11.193%   $67.1272   $67.13   $67.15   $67.10  
  7 purchase totals = $947.82       $1,026.8851   $1,026.89   $1,026.95   $1,026.80