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 $123.73   3.242%   $127.7413   $127.74   $127.75   $127.70  
  Purchase #2 $186.92   12.805%   $210.8551   $210.86   $210.85   $210.90  
  Purchase #3 $66.42   6.544%   $70.7665   $70.77   $70.75   $70.80  
  Purchase #4 $232.88   8.613%   $252.938   $252.94   $252.95   $252.90  
  Purchase #5 $221.82   5.353%   $233.694   $233.69   $233.70   $233.70  
  Purchase #6 $118.30   9.718%   $129.7964   $129.80   $129.80   $129.80  
  Purchase #7 $205.93   5.399%   $217.0482   $217.05   $217.05   $217.00  
  7 purchase totals = $1,156.00       $1,242.8395   $1,242.85   $1,242.85   $1,242.80