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 $42.40   8.526%   $46.015   $46.02   $46.00   $46.00  
  Purchase #2 $61.77   6.128%   $65.5553   $65.56   $65.55   $65.60  
  Purchase #3 $136.79   11.861%   $153.0147   $153.01   $153.00   $153.00  
  Purchase #4 $71.90   10.345%   $79.3381   $79.34   $79.35   $79.30  
  Purchase #5 $94.79   13.574%   $107.6568   $107.66   $107.65   $107.70  
  Purchase #6 $205.69   13.415%   $233.2833   $233.28   $233.30   $233.30  
  Purchase #7 $250.77   9.412%   $274.3725   $274.37   $274.35   $274.40  
  7 purchase totals = $864.11       $959.2357   $959.24   $959.20   $959.30