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	$170.86	4.673%	$178.8443	$178.84	$178.85	$178.80
Purchase #2	$138.68	3.331%	$143.2994	$143.30	$143.30	$143.30
Purchase #3	$195.36	8.756%	$212.4657	$212.47	$212.45	$212.50
Purchase #4	$86.70	4.598%	$90.6865	$90.69	$90.70	$90.70
Purchase #5	$12.27	8.508%	$13.3139	$13.31	$13.30	$13.30
Purchase #6	$224.43	13.502%	$254.7325	$254.73	$254.75	$254.70
Purchase #7	$200.29	11.786%	$223.8962	$223.90	$223.90	$223.90
7 purchase totals =	$1,028.59		$1,117.2385	$1,117.24	$1,117.25	$1,117.20