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 $60.28   8.496%   $65.4014   $65.40   $65.40   $65.40  
  Purchase #2 $151.36   5.659%   $159.9255   $159.93   $159.95   $159.90  
  Purchase #3 $219.26   11.377%   $244.2052   $244.21   $244.20   $244.20  
  Purchase #4 $152.79   5.171%   $160.6908   $160.69   $160.70   $160.70  
  Purchase #5 $43.61   13.619%   $49.5492   $49.55   $49.55   $49.50  
  Purchase #6 $53.66   7.633%   $57.7559   $57.76   $57.75   $57.80  
  Purchase #7 $16.78   12.313%   $18.8461   $18.85   $18.85   $18.80  
  7 purchase totals = $697.74       $756.3741   $756.39   $756.40   $756.30