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 $244.42   4.236%   $254.7736   $254.77   $254.75   $254.80  
  Purchase #2 $29.82   13.473%   $33.8376   $33.84   $33.85   $33.80  
  Purchase #3 $233.67   10.723%   $258.7264   $258.73   $258.75   $258.70  
  Purchase #4 $136.92   8.453%   $148.4938   $148.49   $148.50   $148.50  
  Purchase #5 $189.65   8.389%   $205.5597   $205.56   $205.55   $205.60  
  Purchase #6 $96.85   6.551%   $103.1946   $103.19   $103.20   $103.20  
  Purchase #7 $6.53   6.151%   $6.9317   $6.93   $6.95   $6.90  
  7 purchase totals = $937.86       $1,011.5174   $1,011.51   $1,011.55   $1,011.50