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	$170.77	9.510%	$187.0102	$187.01	$187.00	$187.00
Purchase #2	$119.81	8.733%	$130.273	$130.27	$130.25	$130.30
Purchase #3	$93.76	13.268%	$106.2001	$106.20	$106.20	$106.20
Purchase #4	$38.65	5.840%	$40.9072	$40.91	$40.90	$40.90
Purchase #5	$109.65	8.672%	$119.1588	$119.16	$119.15	$119.20
Purchase #6	$20.39	9.791%	$22.3864	$22.39	$22.40	$22.40
Purchase #7	$56.83	8.217%	$61.4997	$61.50	$61.50	$61.50
7 purchase totals =	$609.86		$667.4354	$667.44	$667.40	$667.50