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 $205.46   13.237%   $232.6567   $232.66   $232.65   $232.70  
  Purchase #2 $158.65   11.719%   $177.2422   $177.24   $177.25   $177.20  
  Purchase #3 $196.49   3.845%   $204.045   $204.05   $204.05   $204.00  
  Purchase #4 $51.38   12.620%   $57.8642   $57.86   $57.85   $57.90  
  Purchase #5 $199.31   4.526%   $208.3308   $208.33   $208.35   $208.30  
  Purchase #6 $54.39   4.757%   $56.9773   $56.98   $57.00   $57.00  
  Purchase #7 $22.57   7.622%   $24.2903   $24.29   $24.30   $24.30  
  7 purchase totals = $888.25       $961.4065   $961.41   $961.45   $961.40