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 $182.76   12.452%   $205.5173   $205.52   $205.50   $205.50  
  Purchase #2 $7.83   4.651%   $8.1942   $8.19   $8.20   $8.20  
  Purchase #3 $110.92   13.538%   $125.9363   $125.94   $125.95   $125.90  
  Purchase #4 $55.56   11.382%   $61.8838   $61.88   $61.90   $61.90  
  Purchase #5 $218.56   8.468%   $237.0677   $237.07   $237.05   $237.10  
  Purchase #6 $98.48   6.790%   $105.1668   $105.17   $105.15   $105.20  
  Purchase #7 $10.59   13.343%   $12.003   $12.00   $12.00   $12.00  
  7 purchase totals = $684.70       $755.7691   $755.77   $755.75   $755.80