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 $63.40   12.264%   $71.1754   $71.18   $71.20   $71.20  
  Purchase #2 $189.71   13.298%   $214.9376   $214.94   $214.95   $214.90  
  Purchase #3 $229.75   8.754%   $249.8623   $249.86   $249.85   $249.90  
  Purchase #4 $178.94   9.392%   $195.746   $195.75   $195.75   $195.70  
  Purchase #5 $232.31   10.767%   $257.3228   $257.32   $257.30   $257.30  
  Purchase #6 $124.71   5.197%   $131.1912   $131.19   $131.20   $131.20  
  Purchase #7 $151.73   6.673%   $161.8549   $161.85   $161.85   $161.90  
  7 purchase totals = $1,170.55       $1,282.0902   $1,282.09   $1,282.10   $1,282.10