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 $241.66   9.124%   $263.7091   $263.71   $263.70   $263.70  
  Purchase #2 $230.91   4.648%   $241.6427   $241.64   $241.65   $241.60  
  Purchase #3 $206.83   8.435%   $224.2761   $224.28   $224.30   $224.30  
  Purchase #4 $244.29   12.632%   $275.1487   $275.15   $275.15   $275.10  
  Purchase #5 $179.97   11.228%   $200.177   $200.18   $200.20   $200.20  
  Purchase #6 $213.65   9.852%   $234.6988   $234.70   $234.70   $234.70  
  Purchase #7 $221.94   9.386%   $242.7713   $242.77   $242.75   $242.80  
  7 purchase totals = $1,539.25       $1,682.4237   $1,682.43   $1,682.45   $1,682.40