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 $247.27   11.219%   $275.0112   $275.01   $275.00   $275.00  
  Purchase #2 $159.87   8.443%   $173.3678   $173.37   $173.35   $173.40  
  Purchase #3 $216.32   4.312%   $225.6477   $225.65   $225.65   $225.60  
  Purchase #4 $51.43   9.415%   $56.2721   $56.27   $56.25   $56.30  
  Purchase #5 $138.69   11.172%   $154.1844   $154.18   $154.20   $154.20  
  Purchase #6 $73.86   10.396%   $81.5385   $81.54   $81.55   $81.50  
  Purchase #7 $236.60   6.515%   $252.0145   $252.01   $252.00   $252.00  
  7 purchase totals = $1,124.04       $1,218.0362   $1,218.03   $1,218.00   $1,218.00