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 $245.97   5.692%   $259.9706   $259.97   $259.95   $260.00  
  Purchase #2 $191.96   12.724%   $216.385   $216.39   $216.40   $216.40  
  Purchase #3 $116.37   11.521%   $129.777   $129.78   $129.80   $129.80  
  Purchase #4 $126.35   5.286%   $133.0289   $133.03   $133.05   $133.00  
  Purchase #5 $107.91   7.771%   $116.2957   $116.30   $116.30   $116.30  
  Purchase #6 $76.33   11.634%   $85.2102   $85.21   $85.20   $85.20  
  Purchase #7 $135.71   7.682%   $146.1352   $146.14   $146.15   $146.10  
  7 purchase totals = $1,000.60       $1,086.8026   $1,086.82   $1,086.85   $1,086.80