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	$147.35	13.359%	$167.0345	$167.03	$167.05	$167.00
Purchase #2	$121.30	13.573%	$137.764	$137.76	$137.75	$137.80
Purchase #3	$111.73	5.156%	$117.4908	$117.49	$117.50	$117.50
Purchase #4	$214.75	3.660%	$222.6099	$222.61	$222.60	$222.60
Purchase #5	$57.76	3.285%	$59.6574	$59.66	$59.65	$59.70
Purchase #6	$170.85	8.474%	$185.3278	$185.33	$185.35	$185.30
Purchase #7	$13.38	5.803%	$14.1564	$14.16	$14.15	$14.20
7 purchase totals =	$837.12		$904.0408	$904.04	$904.05	$904.10