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 $48.66   13.124%   $55.0461   $55.05   $55.05   $55.00  
  Purchase #2 $138.81   4.143%   $144.5609   $144.56   $144.55   $144.60  
  Purchase #3 $118.86   11.195%   $132.1664   $132.17   $132.15   $132.20  
  Purchase #4 $182.86   11.536%   $203.9547   $203.95   $203.95   $204.00  
  Purchase #5 $201.33   9.246%   $219.945   $219.95   $219.95   $219.90  
  Purchase #6 $189.37   9.171%   $206.7371   $206.74   $206.75   $206.70  
  Purchase #7 $207.55   3.550%   $214.918   $214.92   $214.90   $214.90  
  7 purchase totals = $1,087.44       $1,177.3282   $1,177.34   $1,177.30   $1,177.30