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 $34.82   6.261%   $37.0001   $37.00   $37.00   $37.00  
  Purchase #2 $100.53   12.576%   $113.1727   $113.17   $113.15   $113.20  
  Purchase #3 $24.75   11.461%   $27.5866   $27.59   $27.60   $27.60  
  Purchase #4 $186.70   10.203%   $205.749   $205.75   $205.75   $205.70  
  Purchase #5 $157.57   7.274%   $169.0316   $169.03   $169.05   $169.00  
  Purchase #6 $206.84   13.438%   $234.6352   $234.64   $234.65   $234.60  
  Purchase #7 $155.95   12.814%   $175.9334   $175.93   $175.95   $175.90  
  7 purchase totals = $867.16       $963.1086   $963.11   $963.15   $963.00