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 $73.64   13.480%   $83.5667   $83.57   $83.55   $83.60  
  Purchase #2 $216.62   11.120%   $240.7081   $240.71   $240.70   $240.70  
  Purchase #3 $100.28   12.673%   $112.9885   $112.99   $113.00   $113.00  
  Purchase #4 $138.94   6.686%   $148.2295   $148.23   $148.25   $148.20  
  Purchase #5 $53.57   10.291%   $59.0829   $59.08   $59.10   $59.10  
  Purchase #6 $91.29   8.124%   $98.7064   $98.71   $98.70   $98.70  
  Purchase #7 $195.27   13.794%   $222.2055   $222.21   $222.20   $222.20  
  7 purchase totals = $869.61       $965.4876   $965.50   $965.50   $965.50