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 $103.44   12.731%   $116.6089   $116.61   $116.60   $116.60  
  Purchase #2 $62.93   5.494%   $66.3874   $66.39   $66.40   $66.40  
  Purchase #3 $147.62   13.763%   $167.9369   $167.94   $167.95   $167.90  
  Purchase #4 $216.53   13.854%   $246.5281   $246.53   $246.55   $246.50  
  Purchase #5 $94.73   9.798%   $104.0116   $104.01   $104.00   $104.00  
  Purchase #6 $206.92   8.216%   $223.9205   $223.92   $223.90   $223.90  
  Purchase #7 $47.68   13.148%   $53.949   $53.95   $53.95   $53.90  
  7 purchase totals = $879.85       $979.3424   $979.35   $979.35   $979.20