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	$133.58	8.181%	$144.5082	$144.51	$144.50	$144.50
Purchase #2	$123.72	11.851%	$138.3821	$138.38	$138.40	$138.40
Purchase #3	$79.89	6.690%	$85.2346	$85.23	$85.25	$85.20
Purchase #4	$59.26	9.571%	$64.9318	$64.93	$64.95	$64.90
Purchase #5	$71.68	8.266%	$77.6051	$77.61	$77.60	$77.60
Purchase #6	$98.37	3.137%	$101.4559	$101.46	$101.45	$101.50
Purchase #7	$194.73	8.243%	$210.7816	$210.78	$210.80	$210.80
7 purchase totals =	$761.23		$822.8993	$822.90	$822.95	$822.90