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 $229.71   12.605%   $258.6649   $258.66   $258.65   $258.70  
  Purchase #2 $124.54   4.674%   $130.361   $130.36   $130.35   $130.40  
  Purchase #3 $168.69   8.734%   $183.4234   $183.42   $183.40   $183.40  
  Purchase #4 $51.87   8.222%   $56.1348   $56.13   $56.15   $56.10  
  Purchase #5 $118.83   4.399%   $124.0573   $124.06   $124.05   $124.10  
  Purchase #6 $197.77   11.569%   $220.65   $220.65   $220.65   $220.70  
  Purchase #7 $68.43   5.226%   $72.0062   $72.01   $72.00   $72.00  
  7 purchase totals = $959.84       $1,045.2976   $1,045.29   $1,045.25   $1,045.40