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 $209.93   13.820%   $238.9423   $238.94   $238.95   $238.90  
  Purchase #2 $62.79   7.214%   $67.3197   $67.32   $67.30   $67.30  
  Purchase #3 $124.95   12.858%   $141.0161   $141.02   $141.00   $141.00  
  Purchase #4 $203.35   5.639%   $214.8169   $214.82   $214.80   $214.80  
  Purchase #5 $62.74   8.634%   $68.157   $68.16   $68.15   $68.20  
  Purchase #6 $151.30   11.864%   $169.2502   $169.25   $169.25   $169.30  
  Purchase #7 $200.41   12.356%   $225.1727   $225.17   $225.15   $225.20  
  7 purchase totals = $1,015.47       $1,124.6749   $1,124.68   $1,124.60   $1,124.70