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 $157.63   4.718%   $165.067   $165.07   $165.05   $165.10  
  Purchase #2 $58.68   8.525%   $63.6825   $63.68   $63.70   $63.70  
  Purchase #3 $67.47   5.237%   $71.0034   $71.00   $71.00   $71.00  
  Purchase #4 $37.94   3.300%   $39.192   $39.19   $39.20   $39.20  
  Purchase #5 $39.71   9.718%   $43.569   $43.57   $43.55   $43.60  
  Purchase #6 $114.66   10.354%   $126.5319   $126.53   $126.55   $126.50  
  Purchase #7 $231.71   5.433%   $244.2988   $244.30   $244.30   $244.30  
  7 purchase totals = $707.80       $753.3446   $753.34   $753.35   $753.40