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 $203.74   10.283%   $224.6906   $224.69   $224.70   $224.70  
  Purchase #2 $175.42   5.465%   $185.0067   $185.01   $185.00   $185.00  
  Purchase #3 $249.91   4.584%   $261.3659   $261.37   $261.35   $261.40  
  Purchase #4 $61.57   5.130%   $64.7285   $64.73   $64.75   $64.70  
  Purchase #5 $200.56   7.128%   $214.8559   $214.86   $214.85   $214.90  
  Purchase #6 $233.33   5.417%   $245.9695   $245.97   $245.95   $246.00  
  Purchase #7 $183.78   6.709%   $196.1098   $196.11   $196.10   $196.10  
  7 purchase totals = $1,308.31       $1,392.7269   $1,392.74   $1,392.70   $1,392.80