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	$21.57	5.725%	$22.8049	$22.80	$22.80	$22.80
Purchase #2	$59.52	13.643%	$67.6403	$67.64	$67.65	$67.60
Purchase #3	$72.96	5.301%	$76.8276	$76.83	$76.85	$76.80
Purchase #4	$135.78	11.229%	$151.0267	$151.03	$151.05	$151.00
Purchase #5	$152.29	11.833%	$170.3105	$170.31	$170.30	$170.30
Purchase #6	$141.50	6.456%	$150.6352	$150.64	$150.65	$150.60
Purchase #7	$143.68	11.393%	$160.0495	$160.05	$160.05	$160.00
7 purchase totals =	$727.30		$799.2947	$799.30	$799.35	$799.10