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	$88.71	4.274%	$92.5015	$92.50	$92.50	$92.50
Purchase #2	$222.59	9.764%	$244.3237	$244.32	$244.30	$244.30
Purchase #3	$138.56	10.355%	$152.9079	$152.91	$152.90	$152.90
Purchase #4	$19.40	7.843%	$20.9215	$20.92	$20.90	$20.90
Purchase #5	$74.34	4.262%	$77.5084	$77.51	$77.50	$77.50
Purchase #6	$45.78	9.165%	$49.9757	$49.98	$50.00	$50.00
Purchase #7	$149.68	11.753%	$167.2719	$167.27	$167.25	$167.30
7 purchase totals =	$739.06		$805.4106	$805.41	$805.35	$805.40