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	$85.26	7.190%	$91.3902	$91.39	$91.40	$91.40
Purchase #2	$76.73	4.874%	$80.4698	$80.47	$80.45	$80.50
Purchase #3	$73.98	8.326%	$80.1396	$80.14	$80.15	$80.10
Purchase #4	$44.43	11.233%	$49.4208	$49.42	$49.40	$49.40
Purchase #5	$159.36	5.518%	$168.1535	$168.15	$168.15	$168.20
Purchase #6	$61.94	9.253%	$67.6713	$67.67	$67.65	$67.70
Purchase #7	$79.45	3.350%	$82.1116	$82.11	$82.10	$82.10
7 purchase totals =	$581.15		$619.3568	$619.35	$619.30	$619.40