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 $56.81   4.652%   $59.4528   $59.45   $59.45   $59.50  
  Purchase #2 $194.94   5.769%   $206.1861   $206.19   $206.20   $206.20  
  Purchase #3 $191.84   9.333%   $209.7444   $209.74   $209.75   $209.70  
  Purchase #4 $107.69   13.719%   $122.464   $122.46   $122.45   $122.50  
  Purchase #5 $180.72   6.115%   $191.771   $191.77   $191.75   $191.80  
  Purchase #6 $8.79   11.216%   $9.7759   $9.78   $9.80   $9.80  
  Purchase #7 $120.49   8.766%   $131.0522   $131.05   $131.05   $131.10  
  7 purchase totals = $861.28       $930.4464   $930.44   $930.45   $930.60