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	$185.76	6.200%	$197.2771	$197.28	$197.30	$197.30
Purchase #2	$149.43	10.408%	$164.9827	$164.98	$165.00	$165.00
Purchase #3	$69.63	12.504%	$78.3365	$78.34	$78.35	$78.30
Purchase #4	$76.29	9.795%	$83.7626	$83.76	$83.75	$83.80
Purchase #5	$198.83	3.660%	$206.1072	$206.11	$206.10	$206.10
Purchase #6	$85.30	12.103%	$95.6239	$95.62	$95.60	$95.60
Purchase #7	$139.54	11.383%	$155.4238	$155.42	$155.40	$155.40
7 purchase totals =	$904.78		$981.5138	$981.51	$981.50	$981.50