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	$161.56	6.740%	$172.4491	$172.45	$172.45	$172.40
Purchase #2	$223.85	4.491%	$233.9031	$233.90	$233.90	$233.90
Purchase #3	$234.54	8.142%	$253.6362	$253.64	$253.65	$253.60
Purchase #4	$72.36	13.444%	$82.0881	$82.09	$82.10	$82.10
Purchase #5	$120.71	7.560%	$129.8357	$129.84	$129.85	$129.80
Purchase #6	$71.32	6.683%	$76.0863	$76.09	$76.10	$76.10
Purchase #7	$85.42	6.736%	$91.1739	$91.17	$91.15	$91.20
7 purchase totals =	$969.76		$1,039.1724	$1,039.18	$1,039.20	$1,039.10