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 $56.34   5.808%   $59.6122   $59.61   $59.60   $59.60  
  Purchase #2 $65.84   5.872%   $69.7061   $69.71   $69.70   $69.70  
  Purchase #3 $67.43   7.564%   $72.5304   $72.53   $72.55   $72.50  
  Purchase #4 $140.27   9.291%   $153.3025   $153.30   $153.30   $153.30  
  Purchase #5 $240.84   4.511%   $251.7043   $251.70   $251.70   $251.70  
  Purchase #6 $222.89   9.584%   $244.2518   $244.25   $244.25   $244.30  
  Purchase #7 $82.35   5.760%   $87.0934   $87.09   $87.10   $87.10  
  7 purchase totals = $875.96       $938.2007   $938.19   $938.20   $938.20