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 $82.59   12.404%   $92.8345   $92.83   $92.85   $92.80  
  Purchase #2 $195.85   10.693%   $216.7922   $216.79   $216.80   $216.80  
  Purchase #3 $61.86   12.312%   $69.4762   $69.48   $69.50   $69.50  
  Purchase #4 $250.55   11.809%   $280.1374   $280.14   $280.15   $280.10  
  Purchase #5 $159.74   6.548%   $170.1998   $170.20   $170.20   $170.20  
  Purchase #6 $163.41   12.743%   $184.2333   $184.23   $184.25   $184.20  
  Purchase #7 $78.99   12.411%   $88.7934   $88.79   $88.80   $88.80  
  7 purchase totals = $992.99       $1,102.4668   $1,102.46   $1,102.55   $1,102.40