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 $61.64   11.495%   $68.7255   $68.73   $68.75   $68.70  
  Purchase #2 $99.66   4.771%   $104.4148   $104.41   $104.40   $104.40  
  Purchase #3 $226.43   10.801%   $250.8867   $250.89   $250.90   $250.90  
  Purchase #4 $246.84   12.724%   $278.2479   $278.25   $278.25   $278.20  
  Purchase #5 $13.96   6.298%   $14.8392   $14.84   $14.85   $14.80  
  Purchase #6 $180.40   9.223%   $197.0383   $197.04   $197.05   $197.00  
  Purchase #7 $120.41   9.665%   $132.0476   $132.05   $132.05   $132.00  
  7 purchase totals = $949.34       $1,046.2000   $1,046.21   $1,046.25   $1,046.00