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 $57.68   13.155%   $65.2678   $65.27   $65.25   $65.30  
  Purchase #2 $158.76   3.523%   $164.3531   $164.35   $164.35   $164.40  
  Purchase #3 $67.83   11.139%   $75.3856   $75.39   $75.40   $75.40  
  Purchase #4 $100.95   9.607%   $110.6483   $110.65   $110.65   $110.60  
  Purchase #5 $158.26   6.714%   $168.8856   $168.89   $168.90   $168.90  
  Purchase #6 $206.34   9.569%   $226.0847   $226.08   $226.10   $226.10  
  Purchase #7 $10.43   12.185%   $11.7009   $11.70   $11.70   $11.70  
  7 purchase totals = $760.25       $822.3260   $822.33   $822.35   $822.40