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 $61.84   10.695%   $68.4538   $68.45   $68.45   $68.50  
  Purchase #2 $182.71   3.394%   $188.9112   $188.91   $188.90   $188.90  
  Purchase #3 $41.74   10.471%   $46.1106   $46.11   $46.10   $46.10  
  Purchase #4 $183.92   5.114%   $193.3257   $193.33   $193.35   $193.30  
  Purchase #5 $32.89   10.793%   $36.4398   $36.44   $36.45   $36.40  
  Purchase #6 $48.82   7.156%   $52.3136   $52.31   $52.30   $52.30  
  Purchase #7 $208.34   12.313%   $233.9929   $233.99   $234.00   $234.00  
  7 purchase totals = $760.26       $819.5476   $819.54   $819.55   $819.50