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	$247.74	3.637%	$256.7503	$256.75	$256.75	$256.80
Purchase #2	$69.97	12.289%	$78.5686	$78.57	$78.55	$78.60
Purchase #3	$167.59	7.336%	$179.8844	$179.88	$179.90	$179.90
Purchase #4	$35.77	12.477%	$40.233	$40.23	$40.25	$40.20
Purchase #5	$55.60	8.377%	$60.2576	$60.26	$60.25	$60.30
Purchase #6	$180.64	5.251%	$190.1254	$190.13	$190.15	$190.10
Purchase #7	$144.47	4.190%	$150.5233	$150.52	$150.50	$150.50
7 purchase totals =	$901.78		$956.3426	$956.34	$956.35	$956.40