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 $111.56   13.115%   $126.1911   $126.19   $126.20   $126.20  
  Purchase #2 $53.71   9.362%   $58.7383   $58.74   $58.75   $58.70  
  Purchase #3 $192.96   8.681%   $209.7109   $209.71   $209.70   $209.70  
  Purchase #4 $45.94   6.140%   $48.7607   $48.76   $48.75   $48.80  
  Purchase #5 $17.50   11.191%   $19.4584   $19.46   $19.45   $19.50  
  Purchase #6 $67.46   5.486%   $71.1609   $71.16   $71.15   $71.20  
  Purchase #7 $155.42   4.435%   $162.3129   $162.31   $162.30   $162.30  
  7 purchase totals = $644.55       $696.3332   $696.33   $696.30   $696.40