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	$138.31	8.524%	$150.0995	$150.10	$150.10	$150.10
Purchase #2	$154.38	11.849%	$172.6725	$172.67	$172.65	$172.70
Purchase #3	$229.57	5.460%	$242.1045	$242.10	$242.10	$242.10
Purchase #4	$130.90	10.743%	$144.9626	$144.96	$144.95	$145.00
Purchase #5	$135.72	11.721%	$151.6277	$151.63	$151.65	$151.60
Purchase #6	$119.29	13.502%	$135.3965	$135.40	$135.40	$135.40
Purchase #7	$100.89	10.539%	$111.5228	$111.52	$111.50	$111.50
7 purchase totals =	$1,009.06		$1,108.3861	$1,108.38	$1,108.35	$1,108.40