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	$70.90	10.420%	$78.2878	$78.29	$78.30	$78.30
Purchase #2	$74.66	7.558%	$80.3028	$80.30	$80.30	$80.30
Purchase #3	$127.76	3.715%	$132.5063	$132.51	$132.50	$132.50
Purchase #4	$18.86	7.312%	$20.239	$20.24	$20.25	$20.20
Purchase #5	$228.57	6.546%	$243.5322	$243.53	$243.55	$243.50
Purchase #6	$147.63	8.718%	$160.5004	$160.50	$160.50	$160.50
Purchase #7	$172.25	6.196%	$182.9226	$182.92	$182.90	$182.90
7 purchase totals =	$840.63		$898.2911	$898.29	$898.30	$898.20