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	$100.25	13.180%	$113.463	$113.46	$113.45	$113.50
Purchase #2	$79.78	6.708%	$85.1316	$85.13	$85.15	$85.10
Purchase #3	$209.30	11.436%	$233.2355	$233.24	$233.25	$233.20
Purchase #4	$101.53	7.504%	$109.1488	$109.15	$109.15	$109.10
Purchase #5	$32.60	10.146%	$35.9076	$35.91	$35.90	$35.90
Purchase #6	$116.54	5.402%	$122.8355	$122.84	$122.85	$122.80
Purchase #7	$112.70	11.483%	$125.6413	$125.64	$125.65	$125.60
7 purchase totals =	$752.70		$825.3633	$825.37	$825.40	$825.20