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 $54.90   9.807%   $60.284   $60.28   $60.30   $60.30  
  Purchase #2 $158.39   6.672%   $168.9578   $168.96   $168.95   $169.00  
  Purchase #3 $238.39   3.189%   $245.9923   $245.99   $246.00   $246.00  
  Purchase #4 $135.40   8.104%   $146.3728   $146.37   $146.35   $146.40  
  Purchase #5 $95.92   7.634%   $103.2425   $103.24   $103.25   $103.20  
  Purchase #6 $83.79   13.726%   $95.291   $95.29   $95.30   $95.30  
  Purchase #7 $167.71   10.567%   $185.4319   $185.43   $185.45   $185.40  
  7 purchase totals = $934.50       $1,005.5723   $1,005.56   $1,005.60   $1,005.60