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 $114.87   10.471%   $126.898   $126.90   $126.90   $126.90  
  Purchase #2 $58.45   10.332%   $64.4891   $64.49   $64.50   $64.50  
  Purchase #3 $74.46   9.618%   $81.6216   $81.62   $81.60   $81.60  
  Purchase #4 $28.42   4.340%   $29.6534   $29.65   $29.65   $29.70  
  Purchase #5 $57.95   5.365%   $61.059   $61.06   $61.05   $61.10  
  Purchase #6 $33.37   11.214%   $37.1121   $37.11   $37.10   $37.10  
  Purchase #7 $204.92   6.278%   $217.7849   $217.78   $217.80   $217.80  
  7 purchase totals = $572.44       $618.6181   $618.61   $618.60   $618.70