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 $60.29   5.257%   $63.4594   $63.46   $63.45   $63.50  
  Purchase #2 $30.46   11.110%   $33.8441   $33.84   $33.85   $33.80  
  Purchase #3 $165.77   3.111%   $170.9271   $170.93   $170.95   $170.90  
  Purchase #4 $72.62   13.798%   $82.6401   $82.64   $82.65   $82.60  
  Purchase #5 $50.61   8.688%   $55.007   $55.01   $55.00   $55.00  
  Purchase #6 $97.82   5.566%   $103.2647   $103.26   $103.25   $103.30  
  Purchase #7 $14.79   13.569%   $16.7969   $16.80   $16.80   $16.80  
  7 purchase totals = $492.36       $525.9393   $525.94   $525.95   $525.90