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 $177.93   13.719%   $202.3402   $202.34   $202.35   $202.30  
  Purchase #2 $72.71   11.487%   $81.0622   $81.06   $81.05   $81.10  
  Purchase #3 $180.25   5.339%   $189.8735   $189.87   $189.85   $189.90  
  Purchase #4 $128.55   8.383%   $139.3263   $139.33   $139.35   $139.30  
  Purchase #5 $156.34   8.485%   $169.6054   $169.61   $169.60   $169.60  
  Purchase #6 $144.55   4.608%   $151.2109   $151.21   $151.20   $151.20  
  Purchase #7 $23.67   5.173%   $24.8944   $24.89   $24.90   $24.90  
  7 purchase totals = $884.00       $958.3129   $958.31   $958.30   $958.30