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	$25.64	8.450%	$27.8066	$27.81	$27.80	$27.80
Purchase #2	$237.92	5.283%	$250.4893	$250.49	$250.50	$250.50
Purchase #3	$28.55	3.280%	$29.4864	$29.49	$29.50	$29.50
Purchase #4	$105.31	6.865%	$112.5395	$112.54	$112.55	$112.50
Purchase #5	$95.50	11.764%	$106.7346	$106.73	$106.75	$106.70
Purchase #6	$162.95	10.369%	$179.8463	$179.85	$179.85	$179.80
Purchase #7	$158.63	5.626%	$167.5545	$167.55	$167.55	$167.60
7 purchase totals =	$814.50		$874.4572	$874.46	$874.50	$874.40