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 $179.92   13.793%   $204.7364   $204.74   $204.75   $204.70  
  Purchase #2 $66.82   6.190%   $70.9562   $70.96   $70.95   $71.00  
  Purchase #3 $240.87   5.607%   $254.3756   $254.38   $254.40   $254.40  
  Purchase #4 $175.55   8.759%   $190.9264   $190.93   $190.95   $190.90  
  Purchase #5 $229.87   13.581%   $261.0886   $261.09   $261.10   $261.10  
  Purchase #6 $227.59   10.345%   $251.1342   $251.13   $251.15   $251.10  
  Purchase #7 $202.53   4.125%   $210.8844   $210.88   $210.90   $210.90  
  7 purchase totals = $1,323.15       $1,444.1018   $1,444.11   $1,444.20   $1,444.10