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 $194.47   7.104%   $208.2851   $208.29   $208.30   $208.30  
  Purchase #2 $33.71   11.258%   $37.5051   $37.51   $37.50   $37.50  
  Purchase #3 $69.47   8.661%   $75.4868   $75.49   $75.50   $75.50  
  Purchase #4 $190.78   7.802%   $205.6647   $205.66   $205.65   $205.70  
  Purchase #5 $234.91   13.129%   $265.7513   $265.75   $265.75   $265.80  
  Purchase #6 $98.41   7.310%   $105.6038   $105.60   $105.60   $105.60  
  Purchase #7 $118.79   5.184%   $124.9481   $124.95   $124.95   $124.90  
  7 purchase totals = $940.54       $1,023.2449   $1,023.25   $1,023.25   $1,023.30