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 $230.54   12.228%   $258.7304   $258.73   $258.75   $258.70  
  Purchase #2 $67.94   13.249%   $76.9414   $76.94   $76.95   $76.90  
  Purchase #3 $86.93   5.234%   $91.4799   $91.48   $91.50   $91.50  
  Purchase #4 $175.78   13.538%   $199.5771   $199.58   $199.60   $199.60  
  Purchase #5 $236.96   13.288%   $268.4472   $268.45   $268.45   $268.40  
  Purchase #6 $163.31   7.771%   $176.0008   $176.00   $176.00   $176.00  
  Purchase #7 $30.26   5.156%   $31.8202   $31.82   $31.80   $31.80  
  7 purchase totals = $991.72       $1,102.9970   $1,103.00   $1,103.05   $1,102.90