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	$124.43	4.301%	$129.7817	$129.78	$129.80	$129.80
Purchase #2	$165.35	13.242%	$187.2456	$187.25	$187.25	$187.20
Purchase #3	$124.38	13.690%	$141.4076	$141.41	$141.40	$141.40
Purchase #4	$34.36	9.285%	$37.5503	$37.55	$37.55	$37.60
Purchase #5	$156.87	4.700%	$164.2429	$164.24	$164.25	$164.20
Purchase #6	$139.53	12.483%	$156.9475	$156.95	$156.95	$156.90
Purchase #7	$11.50	5.142%	$12.0913	$12.09	$12.10	$12.10
7 purchase totals =	$756.42		$829.2669	$829.27	$829.30	$829.20