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 $195.85   12.295%   $219.9298   $219.93   $219.95   $219.90  
  Purchase #2 $228.51   13.799%   $260.0421   $260.04   $260.05   $260.00  
  Purchase #3 $222.63   8.608%   $241.794   $241.79   $241.80   $241.80  
  Purchase #4 $166.79   7.289%   $178.9473   $178.95   $178.95   $178.90  
  Purchase #5 $204.75   9.531%   $224.2647   $224.26   $224.25   $224.30  
  Purchase #6 $212.76   12.479%   $239.3103   $239.31   $239.30   $239.30  
  Purchase #7 $12.99   10.541%   $14.3593   $14.36   $14.35   $14.40  
  7 purchase totals = $1,244.28       $1,378.6475   $1,378.64   $1,378.65   $1,378.60