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 $191.38   5.395%   $201.705   $201.71   $201.70   $201.70  
  Purchase #2 $33.94   10.480%   $37.4969   $37.50   $37.50   $37.50  
  Purchase #3 $230.56   9.173%   $251.7093   $251.71   $251.70   $251.70  
  Purchase #4 $60.56   4.742%   $63.4318   $63.43   $63.45   $63.40  
  Purchase #5 $182.67   6.172%   $193.9444   $193.94   $193.95   $193.90  
  Purchase #6 $56.28   7.391%   $60.4397   $60.44   $60.45   $60.40  
  Purchase #7 $140.54   4.253%   $146.5172   $146.52   $146.50   $146.50  
  7 purchase totals = $895.93       $955.2443   $955.25   $955.25   $955.10