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 $67.99   11.327%   $75.6912   $75.69   $75.70   $75.70  
  Purchase #2 $227.87   3.595%   $236.0619   $236.06   $236.05   $236.10  
  Purchase #3 $153.62   5.370%   $161.8694   $161.87   $161.85   $161.90  
  Purchase #4 $246.60   13.303%   $279.4052   $279.41   $279.40   $279.40  
  Purchase #5 $94.68   12.507%   $106.5216   $106.52   $106.50   $106.50  
  Purchase #6 $140.93   11.627%   $157.3159   $157.32   $157.30   $157.30  
  Purchase #7 $136.48   8.611%   $148.2323   $148.23   $148.25   $148.20  
  7 purchase totals = $1,068.17       $1,165.0975   $1,165.10   $1,165.05   $1,165.10