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 $84.51   12.616%   $95.1718   $95.17   $95.15   $95.20  
  Purchase #2 $27.77   7.204%   $29.7706   $29.77   $29.75   $29.80  
  Purchase #3 $140.42   8.594%   $152.4877   $152.49   $152.50   $152.50  
  Purchase #4 $53.95   12.205%   $60.5346   $60.53   $60.55   $60.50  
  Purchase #5 $228.98   7.572%   $246.3184   $246.32   $246.30   $246.30  
  Purchase #6 $126.92   8.339%   $137.5039   $137.50   $137.50   $137.50  
  Purchase #7 $215.88   9.201%   $235.7431   $235.74   $235.75   $235.70  
  7 purchase totals = $878.43       $957.5301   $957.52   $957.50   $957.50