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	$17.25	8.451%	$18.7078	$18.71	$18.70	$18.70
Purchase #2	$187.54	11.256%	$208.6495	$208.65	$208.65	$208.60
Purchase #3	$92.80	6.234%	$98.5852	$98.59	$98.60	$98.60
Purchase #4	$89.60	11.430%	$99.8413	$99.84	$99.85	$99.80
Purchase #5	$106.74	9.559%	$116.9433	$116.94	$116.95	$116.90
Purchase #6	$137.26	9.839%	$150.765	$150.77	$150.75	$150.80
Purchase #7	$211.89	4.313%	$221.0288	$221.03	$221.05	$221.00
7 purchase totals =	$843.08		$914.5209	$914.53	$914.55	$914.40