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 $181.52   12.459%   $204.1356   $204.14   $204.15   $204.10  
  Purchase #2 $211.42   6.117%   $224.3526   $224.35   $224.35   $224.40  
  Purchase #3 $181.84   13.258%   $205.9483   $205.95   $205.95   $205.90  
  Purchase #4 $29.36   11.699%   $32.7948   $32.79   $32.80   $32.80  
  Purchase #5 $216.84   13.165%   $245.387   $245.39   $245.40   $245.40  
  Purchase #6 $64.89   8.320%   $70.2888   $70.29   $70.30   $70.30  
  Purchase #7 $240.81   8.511%   $261.3053   $261.31   $261.30   $261.30  
  7 purchase totals = $1,126.68       $1,244.2124   $1,244.22   $1,244.25   $1,244.20