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 $59.36   11.216%   $66.0178   $66.02   $66.00   $66.00  
  Purchase #2 $136.80   9.419%   $149.6852   $149.69   $149.70   $149.70  
  Purchase #3 $157.48   6.506%   $167.7256   $167.73   $167.75   $167.70  
  Purchase #4 $22.85   4.139%   $23.7958   $23.80   $23.80   $23.80  
  Purchase #5 $182.95   13.138%   $206.986   $206.99   $207.00   $207.00  
  Purchase #6 $47.77   6.838%   $51.0365   $51.04   $51.05   $51.00  
  Purchase #7 $108.60   3.595%   $112.5042   $112.50   $112.50   $112.50  
  7 purchase totals = $715.81       $777.7511   $777.77   $777.80   $777.70