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 $226.97   6.672%   $242.1134   $242.11   $242.10   $242.10  
  Purchase #2 $127.98   10.302%   $141.1645   $141.16   $141.15   $141.20  
  Purchase #3 $34.50   3.171%   $35.594   $35.59   $35.60   $35.60  
  Purchase #4 $212.90   10.355%   $234.9458   $234.95   $234.95   $234.90  
  Purchase #5 $170.53   6.211%   $181.1216   $181.12   $181.10   $181.10  
  Purchase #6 $226.51   13.541%   $257.1817   $257.18   $257.20   $257.20  
  Purchase #7 $62.52   7.602%   $67.2728   $67.27   $67.25   $67.30  
  7 purchase totals = $1,061.91       $1,159.3938   $1,159.38   $1,159.35   $1,159.40