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 $118.84   6.254%   $126.2723   $126.27   $126.25   $126.30  
  Purchase #2 $240.58   13.335%   $272.6613   $272.66   $272.65   $272.70  
  Purchase #3 $221.78   12.242%   $248.9303   $248.93   $248.95   $248.90  
  Purchase #4 $166.82   11.507%   $186.016   $186.02   $186.00   $186.00  
  Purchase #5 $49.51   11.793%   $55.3487   $55.35   $55.35   $55.30  
  Purchase #6 $22.96   13.552%   $26.0715   $26.07   $26.05   $26.10  
  Purchase #7 $22.90   9.389%   $25.0501   $25.05   $25.05   $25.10  
  7 purchase totals = $843.39       $940.3502   $940.35   $940.30   $940.40