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 $73.27   8.453%   $79.4635   $79.46   $79.45   $79.50  
  Purchase #2 $110.96   13.149%   $125.5501   $125.55   $125.55   $125.60  
  Purchase #3 $88.63   12.574%   $99.7743   $99.77   $99.75   $99.80  
  Purchase #4 $231.76   9.381%   $253.5014   $253.50   $253.50   $253.50  
  Purchase #5 $205.38   4.136%   $213.8745   $213.87   $213.85   $213.90  
  Purchase #6 $250.63   13.137%   $283.5553   $283.56   $283.55   $283.60  
  Purchase #7 $160.82   11.861%   $179.8949   $179.89   $179.90   $179.90  
  7 purchase totals = $1,121.45       $1,235.6140   $1,235.60   $1,235.55   $1,235.80