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 $85.58   10.122%   $94.2424   $94.24   $94.25   $94.20  
  Purchase #2 $218.31   4.567%   $228.2802   $228.28   $228.30   $228.30  
  Purchase #3 $247.42   3.128%   $255.1593   $255.16   $255.15   $255.20  
  Purchase #4 $83.39   9.368%   $91.202   $91.20   $91.20   $91.20  
  Purchase #5 $44.63   8.210%   $48.2941   $48.29   $48.30   $48.30  
  Purchase #6 $244.84   12.413%   $275.232   $275.23   $275.25   $275.20  
  Purchase #7 $18.77   6.592%   $20.0073   $20.01   $20.00   $20.00  
  7 purchase totals = $942.94       $1,012.4173   $1,012.41   $1,012.45   $1,012.40