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 $87.73   12.305%   $98.5252   $98.53   $98.55   $98.50  
  Purchase #2 $196.42   6.318%   $208.8298   $208.83   $208.85   $208.80  
  Purchase #3 $196.38   5.345%   $206.8765   $206.88   $206.90   $206.90  
  Purchase #4 $226.77   9.545%   $248.4152   $248.42   $248.40   $248.40  
  Purchase #5 $93.60   9.775%   $102.7494   $102.75   $102.75   $102.70  
  Purchase #6 $25.70   6.700%   $27.4219   $27.42   $27.40   $27.40  
  Purchase #7 $94.74   5.547%   $99.9952   $100.00   $100.00   $100.00  
  7 purchase totals = $921.34       $992.8132   $992.83   $992.85   $992.70