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	$99.69	12.827%	$112.4772	$112.48	$112.50	$112.50
Purchase #2	$105.48	3.533%	$109.2066	$109.21	$109.20	$109.20
Purchase #3	$106.88	11.120%	$118.7651	$118.77	$118.75	$118.80
Purchase #4	$169.55	9.336%	$185.3792	$185.38	$185.40	$185.40
Purchase #5	$157.61	9.543%	$172.6507	$172.65	$172.65	$172.70
Purchase #6	$209.86	12.184%	$235.4293	$235.43	$235.45	$235.40
Purchase #7	$99.77	9.252%	$109.0007	$109.00	$109.00	$109.00
7 purchase totals =	$948.84		$1,042.9088	$1,042.92	$1,042.95	$1,043.00