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 $215.71   8.831%   $234.7594   $234.76   $234.75   $234.80  
  Purchase #2 $39.46   5.787%   $41.7436   $41.74   $41.75   $41.70  
  Purchase #3 $193.25   11.154%   $214.8051   $214.81   $214.80   $214.80  
  Purchase #4 $159.47   4.602%   $166.8088   $166.81   $166.80   $166.80  
  Purchase #5 $157.32   9.774%   $172.6965   $172.70   $172.70   $172.70  
  Purchase #6 $204.79   9.219%   $223.6696   $223.67   $223.65   $223.70  
  Purchase #7 $232.77   12.217%   $261.2075   $261.21   $261.20   $261.20  
  7 purchase totals = $1,202.77       $1,315.6905   $1,315.70   $1,315.65   $1,315.70