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 $93.71   4.227%   $97.6711   $97.67   $97.65   $97.70  
  Purchase #2 $224.37   9.727%   $246.1945   $246.19   $246.20   $246.20  
  Purchase #3 $202.90   5.594%   $214.2502   $214.25   $214.25   $214.30  
  Purchase #4 $17.26   4.677%   $18.0673   $18.07   $18.05   $18.10  
  Purchase #5 $11.69   5.594%   $12.3439   $12.34   $12.35   $12.30  
  Purchase #6 $88.37   7.336%   $94.8528   $94.85   $94.85   $94.90  
  Purchase #7 $117.93   3.132%   $121.6236   $121.62   $121.60   $121.60  
  7 purchase totals = $756.23       $805.0034   $804.99   $804.95   $805.10