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 $222.58   12.723%   $250.8989   $250.90   $250.90   $250.90  
  Purchase #2 $65.34   8.254%   $70.7332   $70.73   $70.75   $70.70  
  Purchase #3 $59.59   12.482%   $67.028   $67.03   $67.05   $67.00  
  Purchase #4 $22.62   13.671%   $25.7124   $25.71   $25.70   $25.70  
  Purchase #5 $103.27   5.762%   $109.2204   $109.22   $109.20   $109.20  
  Purchase #6 $164.51   5.333%   $173.2833   $173.28   $173.30   $173.30  
  Purchase #7 $56.29   6.679%   $60.0496   $60.05   $60.05   $60.00  
  7 purchase totals = $694.20       $756.9258   $756.92   $756.95   $756.80