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	$43.69	4.161%	$45.5079	$45.51	$45.50	$45.50
Purchase #2	$198.69	6.645%	$211.893	$211.89	$211.90	$211.90
Purchase #3	$74.78	11.644%	$83.4874	$83.49	$83.50	$83.50
Purchase #4	$61.98	13.239%	$70.1855	$70.19	$70.20	$70.20
Purchase #5	$227.38	11.787%	$254.1813	$254.18	$254.20	$254.20
Purchase #6	$78.94	6.202%	$83.8359	$83.84	$83.85	$83.80
Purchase #7	$40.41	6.244%	$42.9332	$42.93	$42.95	$42.90
7 purchase totals =	$725.87		$792.0242	$792.03	$792.10	$792.00