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 $138.27   9.424%   $151.3006   $151.30   $151.30   $151.30  
  Purchase #2 $85.77   8.328%   $92.9129   $92.91   $92.90   $92.90  
  Purchase #3 $66.83   12.468%   $75.1624   $75.16   $75.15   $75.20  
  Purchase #4 $232.83   8.349%   $252.269   $252.27   $252.25   $252.30  
  Purchase #5 $163.56   9.611%   $179.2798   $179.28   $179.30   $179.30  
  Purchase #6 $5.99   13.257%   $6.7841   $6.78   $6.80   $6.80  
  Purchase #7 $36.41   3.620%   $37.728   $37.73   $37.75   $37.70  
  7 purchase totals = $729.66       $795.4368   $795.43   $795.45   $795.50