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 $68.74   11.354%   $76.5447   $76.54   $76.55   $76.50  
  Purchase #2 $50.79   8.369%   $55.0406   $55.04   $55.05   $55.00  
  Purchase #3 $212.45   9.718%   $233.0959   $233.10   $233.10   $233.10  
  Purchase #4 $197.65   7.544%   $212.5607   $212.56   $212.55   $212.60  
  Purchase #5 $47.50   5.146%   $49.9444   $49.94   $49.95   $49.90  
  Purchase #6 $86.90   12.569%   $97.8225   $97.82   $97.80   $97.80  
  Purchase #7 $38.37   12.812%   $43.286   $43.29   $43.30   $43.30  
  7 purchase totals = $702.40       $768.2948   $768.29   $768.30   $768.20