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 $244.34   8.445%   $264.9745   $264.97   $264.95   $265.00  
  Purchase #2 $234.61   11.146%   $260.7596   $260.76   $260.75   $260.80  
  Purchase #3 $30.82   3.170%   $31.797   $31.80   $31.80   $31.80  
  Purchase #4 $93.55   9.676%   $102.6019   $102.60   $102.60   $102.60  
  Purchase #5 $123.55   8.377%   $133.8998   $133.90   $133.90   $133.90  
  Purchase #6 $118.98   4.403%   $124.2187   $124.22   $124.20   $124.20  
  Purchase #7 $23.80   4.315%   $24.827   $24.83   $24.85   $24.80  
  7 purchase totals = $869.65       $943.0785   $943.08   $943.05   $943.10