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 $107.86   11.144%   $119.8799   $119.88   $119.90   $119.90  
  Purchase #2 $51.73   5.548%   $54.6   $54.60   $54.60   $54.60  
  Purchase #3 $117.59   8.616%   $127.7216   $127.72   $127.70   $127.70  
  Purchase #4 $121.93   4.752%   $127.7241   $127.72   $127.70   $127.70  
  Purchase #5 $243.82   3.617%   $252.639   $252.64   $252.65   $252.60  
  Purchase #6 $177.45   9.833%   $194.8987   $194.90   $194.90   $194.90  
  Purchase #7 $68.59   10.597%   $75.8585   $75.86   $75.85   $75.90  
  7 purchase totals = $888.97       $953.3218   $953.32   $953.30   $953.30