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	$37.28	7.641%	$40.1286	$40.13	$40.15	$40.10
Purchase #2	$226.84	7.110%	$242.9683	$242.97	$242.95	$243.00
Purchase #3	$64.76	8.541%	$70.2912	$70.29	$70.30	$70.30
Purchase #4	$68.36	6.632%	$72.8936	$72.89	$72.90	$72.90
Purchase #5	$93.83	12.472%	$105.5325	$105.53	$105.55	$105.50
Purchase #6	$144.36	3.328%	$149.1643	$149.16	$149.15	$149.20
Purchase #7	$145.78	5.281%	$153.4786	$153.48	$153.50	$153.50
7 purchase totals =	$781.21		$834.4571	$834.45	$834.50	$834.50