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 $48.77   12.823%   $55.0238   $55.02   $55.00   $55.00  
  Purchase #2 $226.85   11.597%   $253.1578   $253.16   $253.15   $253.20  
  Purchase #3 $140.29   5.758%   $148.3679   $148.37   $148.35   $148.40  
  Purchase #4 $96.56   4.640%   $101.0404   $101.04   $101.05   $101.00  
  Purchase #5 $214.55   6.209%   $227.8714   $227.87   $227.85   $227.90  
  Purchase #6 $217.33   4.356%   $226.7969   $226.80   $226.80   $226.80  
  Purchase #7 $190.68   10.115%   $209.9673   $209.97   $209.95   $210.00  
  7 purchase totals = $1,135.03       $1,222.2255   $1,222.23   $1,222.15   $1,222.30