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 $32.66   4.855%   $34.2456   $34.25   $34.25   $34.20  
  Purchase #2 $224.97   6.870%   $240.4254   $240.43   $240.45   $240.40  
  Purchase #3 $33.94   6.144%   $36.0253   $36.03   $36.05   $36.00  
  Purchase #4 $167.27   3.702%   $173.4623   $173.46   $173.45   $173.50  
  Purchase #5 $163.48   4.596%   $170.9935   $170.99   $171.00   $171.00  
  Purchase #6 $37.37   9.486%   $40.9149   $40.91   $40.90   $40.90  
  Purchase #7 $232.62   12.870%   $262.5582   $262.56   $262.55   $262.60  
  7 purchase totals = $892.31       $958.6252   $958.63   $958.65   $958.60