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 $232.73   10.492%   $257.148   $257.15   $257.15   $257.10  
  Purchase #2 $105.59   10.756%   $116.9473   $116.95   $116.95   $116.90  
  Purchase #3 $227.79   8.244%   $246.569   $246.57   $246.55   $246.60  
  Purchase #4 $233.27   12.364%   $262.1115   $262.11   $262.10   $262.10  
  Purchase #5 $216.64   6.725%   $231.209   $231.21   $231.20   $231.20  
  Purchase #6 $198.26   5.274%   $208.7162   $208.72   $208.70   $208.70  
  Purchase #7 $145.64   4.403%   $152.0525   $152.05   $152.05   $152.10  
  7 purchase totals = $1,359.92       $1,474.7535   $1,474.76   $1,474.70   $1,474.70