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	$78.77	12.484%	$88.6036	$88.60	$88.60	$88.60
Purchase #2	$88.57	11.129%	$98.427	$98.43	$98.45	$98.40
Purchase #3	$98.90	12.499%	$111.2615	$111.26	$111.25	$111.30
Purchase #4	$79.76	12.734%	$89.9166	$89.92	$89.90	$89.90
Purchase #5	$206.78	7.723%	$222.7496	$222.75	$222.75	$222.70
Purchase #6	$169.78	11.227%	$188.8412	$188.84	$188.85	$188.80
Purchase #7	$52.77	6.343%	$56.1172	$56.12	$56.10	$56.10
7 purchase totals =	$775.33		$855.9167	$855.92	$855.90	$855.80