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 $111.62   4.197%   $116.3047   $116.30   $116.30   $116.30  
  Purchase #2 $188.82   3.306%   $195.0624   $195.06   $195.05   $195.10  
  Purchase #3 $67.87   11.517%   $75.6866   $75.69   $75.70   $75.70  
  Purchase #4 $110.66   9.527%   $121.2026   $121.20   $121.20   $121.20  
  Purchase #5 $11.98   9.491%   $13.117   $13.12   $13.10   $13.10  
  Purchase #6 $139.33   12.859%   $157.2464   $157.25   $157.25   $157.20  
  Purchase #7 $19.34   3.121%   $19.9436   $19.94   $19.95   $19.90  
  7 purchase totals = $649.62       $698.5633   $698.56   $698.55   $698.50