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	$67.52	4.427%	$70.5091	$70.51	$70.50	$70.50
Purchase #2	$77.98	12.722%	$87.9006	$87.90	$87.90	$87.90
Purchase #3	$215.29	12.535%	$242.2766	$242.28	$242.30	$242.30
Purchase #4	$50.73	12.140%	$56.8886	$56.89	$56.90	$56.90
Purchase #5	$250.28	11.335%	$278.6492	$278.65	$278.65	$278.60
Purchase #6	$75.52	9.288%	$82.5343	$82.53	$82.55	$82.50
Purchase #7	$109.84	9.250%	$120.0002	$120.00	$120.00	$120.00
7 purchase totals =	$847.16		$938.7586	$938.76	$938.80	$938.70