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	$31.32	12.168%	$35.131	$35.13	$35.15	$35.10
Purchase #2	$229.83	11.560%	$256.3983	$256.40	$256.40	$256.40
Purchase #3	$93.56	7.403%	$100.4862	$100.49	$100.50	$100.50
Purchase #4	$204.51	3.458%	$211.582	$211.58	$211.60	$211.60
Purchase #5	$124.74	12.268%	$140.0431	$140.04	$140.05	$140.00
Purchase #6	$168.60	6.311%	$179.2403	$179.24	$179.25	$179.20
Purchase #7	$33.87	10.736%	$37.5063	$37.51	$37.50	$37.50
7 purchase totals =	$886.43		$960.3872	$960.39	$960.45	$960.30