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 $96.96   9.757%   $106.4204   $106.42   $106.40   $106.40  
  Purchase #2 $67.92   11.857%   $75.9733   $75.97   $75.95   $76.00  
  Purchase #3 $143.51   13.420%   $162.769   $162.77   $162.75   $162.80  
  Purchase #4 $235.93   3.846%   $245.0039   $245.00   $245.00   $245.00  
  Purchase #5 $116.50   13.479%   $132.203   $132.20   $132.20   $132.20  
  Purchase #6 $173.29   12.428%   $194.8265   $194.83   $194.85   $194.80  
  Purchase #7 $232.97   12.584%   $262.2869   $262.29   $262.30   $262.30  
  7 purchase totals = $1,067.08       $1,179.4830   $1,179.48   $1,179.45   $1,179.50