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 $245.53   8.761%   $267.0409   $267.04   $267.05   $267.00  
  Purchase #2 $76.43   11.220%   $85.0054   $85.01   $85.00   $85.00  
  Purchase #3 $217.46   9.684%   $238.5188   $238.52   $238.50   $238.50  
  Purchase #4 $130.86   7.499%   $140.6732   $140.67   $140.65   $140.70  
  Purchase #5 $30.58   6.714%   $32.6331   $32.63   $32.65   $32.60  
  Purchase #6 $228.55   3.382%   $236.2796   $236.28   $236.30   $236.30  
  Purchase #7 $246.54   5.408%   $259.8729   $259.87   $259.85   $259.90  
  7 purchase totals = $1,175.95       $1,260.0239   $1,260.02   $1,260.00   $1,260.00