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 $150.93   10.799%   $167.2289   $167.23   $167.25   $167.20  
  Purchase #2 $153.92   12.577%   $173.2785   $173.28   $173.30   $173.30  
  Purchase #3 $71.35   4.223%   $74.3631   $74.36   $74.35   $74.40  
  Purchase #4 $239.49   6.872%   $255.9478   $255.95   $255.95   $255.90  
  Purchase #5 $170.32   13.454%   $193.2349   $193.23   $193.25   $193.20  
  Purchase #6 $75.32   3.354%   $77.8462   $77.85   $77.85   $77.80  
  Purchase #7 $22.70   7.172%   $24.328   $24.33   $24.35   $24.30  
  7 purchase totals = $884.03       $966.2274   $966.23   $966.30   $966.10