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	$90.39	12.792%	$101.9527	$101.95	$101.95	$102.00
Purchase #2	$59.81	7.703%	$64.4172	$64.42	$64.40	$64.40
Purchase #3	$136.61	6.711%	$145.7779	$145.78	$145.80	$145.80
Purchase #4	$157.30	5.451%	$165.8744	$165.87	$165.85	$165.90
Purchase #5	$67.37	9.381%	$73.69	$73.69	$73.70	$73.70
Purchase #6	$90.77	10.206%	$100.034	$100.03	$100.05	$100.00
Purchase #7	$207.79	10.586%	$229.7866	$229.79	$229.80	$229.80
7 purchase totals =	$810.04		$881.5328	$881.53	$881.55	$881.60