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 $66.94   13.225%   $75.7928   $75.79   $75.80   $75.80  
  Purchase #2 $238.76   11.604%   $266.4657   $266.47   $266.45   $266.50  
  Purchase #3 $51.78   12.390%   $58.1955   $58.20   $58.20   $58.20  
  Purchase #4 $8.85   3.121%   $9.1262   $9.13   $9.15   $9.10  
  Purchase #5 $203.47   5.534%   $214.73   $214.73   $214.75   $214.70  
  Purchase #6 $158.56   4.196%   $165.2132   $165.21   $165.20   $165.20  
  Purchase #7 $129.68   11.197%   $144.2003   $144.20   $144.20   $144.20  
  7 purchase totals = $858.04       $933.7237   $933.73   $933.75   $933.70