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 $15.51   12.663%   $17.474   $17.47   $17.45   $17.50  
  Purchase #2 $241.42   5.326%   $254.278   $254.28   $254.30   $254.30  
  Purchase #3 $233.45   10.176%   $257.2059   $257.21   $257.20   $257.20  
  Purchase #4 $120.65   13.841%   $137.3492   $137.35   $137.35   $137.30  
  Purchase #5 $193.34   8.251%   $209.2925   $209.29   $209.30   $209.30  
  Purchase #6 $235.45   4.867%   $246.9094   $246.91   $246.90   $246.90  
  Purchase #7 $241.94   3.554%   $250.5385   $250.54   $250.55   $250.50  
  7 purchase totals = $1,281.76       $1,373.0475   $1,373.05   $1,373.05   $1,373.00