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 $52.63   11.559%   $58.7135   $58.71   $58.70   $58.70  
  Purchase #2 $112.70   12.143%   $126.3852   $126.39   $126.40   $126.40  
  Purchase #3 $95.90   6.384%   $102.0223   $102.02   $102.00   $102.00  
  Purchase #4 $211.54   11.392%   $235.6386   $235.64   $235.65   $235.60  
  Purchase #5 $85.96   9.632%   $94.2397   $94.24   $94.25   $94.20  
  Purchase #6 $57.85   4.776%   $60.6129   $60.61   $60.60   $60.60  
  Purchase #7 $158.98   7.388%   $170.7254   $170.73   $170.75   $170.70  
  7 purchase totals = $775.56       $848.3376   $848.34   $848.35   $848.20