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 $217.81   12.364%   $244.74   $244.74   $244.75   $244.70  
  Purchase #2 $144.26   5.161%   $151.7053   $151.71   $151.70   $151.70  
  Purchase #3 $189.40   12.202%   $212.5106   $212.51   $212.50   $212.50  
  Purchase #4 $226.26   12.665%   $254.9158   $254.92   $254.90   $254.90  
  Purchase #5 $220.78   9.164%   $241.0123   $241.01   $241.00   $241.00  
  Purchase #6 $193.44   11.231%   $215.1652   $215.17   $215.15   $215.20  
  Purchase #7 $158.28   9.801%   $173.793   $173.79   $173.80   $173.80  
  7 purchase totals = $1,350.23       $1,493.8422   $1,493.85   $1,493.80   $1,493.80