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 $23.29   3.102%   $24.0125   $24.01   $24.00   $24.00  
  Purchase #2 $213.61   10.771%   $236.6179   $236.62   $236.60   $236.60  
  Purchase #3 $243.44   11.447%   $271.3066   $271.31   $271.30   $271.30  
  Purchase #4 $107.30   12.514%   $120.7275   $120.73   $120.75   $120.70  
  Purchase #5 $151.85   5.727%   $160.5464   $160.55   $160.55   $160.50  
  Purchase #6 $201.83   12.109%   $226.2696   $226.27   $226.25   $226.30  
  Purchase #7 $162.48   3.507%   $168.1782   $168.18   $168.20   $168.20  
  7 purchase totals = $1,103.80       $1,207.6587   $1,207.67   $1,207.65   $1,207.60