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 $160.88   6.266%   $170.9607   $170.96   $170.95   $171.00  
  Purchase #2 $31.73   7.163%   $34.0028   $34.00   $34.00   $34.00  
  Purchase #3 $134.31   12.865%   $151.589   $151.59   $151.60   $151.60  
  Purchase #4 $51.28   12.565%   $57.7233   $57.72   $57.70   $57.70  
  Purchase #5 $227.40   11.339%   $253.1849   $253.18   $253.20   $253.20  
  Purchase #6 $84.74   9.376%   $92.6852   $92.69   $92.70   $92.70  
  Purchase #7 $177.67   4.290%   $185.292   $185.29   $185.30   $185.30  
  7 purchase totals = $868.01       $945.4379   $945.43   $945.45   $945.50