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	$89.28	11.606%	$99.6418	$99.64	$99.65	$99.60
Purchase #2	$179.53	6.516%	$191.2282	$191.23	$191.25	$191.20
Purchase #3	$87.85	3.319%	$90.7657	$90.77	$90.75	$90.80
Purchase #4	$249.30	11.156%	$277.1119	$277.11	$277.10	$277.10
Purchase #5	$37.65	12.729%	$42.4425	$42.44	$42.45	$42.40
Purchase #6	$237.71	4.138%	$247.5464	$247.55	$247.55	$247.50
Purchase #7	$38.90	8.749%	$42.3034	$42.30	$42.30	$42.30
7 purchase totals =	$920.22		$991.0399	$991.04	$991.05	$990.90