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 $50.86   4.168%   $52.9798   $52.98   $53.00   $53.00  
  Purchase #2 $229.73   7.676%   $247.3641   $247.36   $247.35   $247.40  
  Purchase #3 $24.72   3.289%   $25.533   $25.53   $25.55   $25.50  
  Purchase #4 $35.55   5.203%   $37.3997   $37.40   $37.40   $37.40  
  Purchase #5 $143.87   7.108%   $154.0963   $154.10   $154.10   $154.10  
  Purchase #6 $177.36   7.135%   $190.0146   $190.01   $190.00   $190.00  
  Purchase #7 $224.27   9.118%   $244.7189   $244.72   $244.70   $244.70  
  7 purchase totals = $886.36       $952.1064   $952.10   $952.10   $952.10