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 $241.71   11.114%   $268.5736   $268.57   $268.55   $268.60  
  Purchase #2 $166.40   9.668%   $182.4876   $182.49   $182.50   $182.50  
  Purchase #3 $246.25   3.267%   $254.295   $254.30   $254.30   $254.30  
  Purchase #4 $59.27   6.157%   $62.9193   $62.92   $62.90   $62.90  
  Purchase #5 $80.93   9.203%   $88.378   $88.38   $88.40   $88.40  
  Purchase #6 $200.54   5.129%   $210.8257   $210.83   $210.85   $210.80  
  Purchase #7 $71.26   7.703%   $76.7492   $76.75   $76.75   $76.70  
  7 purchase totals = $1,066.36       $1,144.2284   $1,144.24   $1,144.25   $1,144.20