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	$87.27	13.345%	$98.9162	$98.92	$98.90	$98.90
Purchase #2	$49.44	10.155%	$54.4606	$54.46	$54.45	$54.50
Purchase #3	$90.84	8.280%	$98.3616	$98.36	$98.35	$98.40
Purchase #4	$126.68	4.629%	$132.544	$132.54	$132.55	$132.50
Purchase #5	$53.94	10.805%	$59.7682	$59.77	$59.75	$59.80
Purchase #6	$180.67	9.720%	$198.2311	$198.23	$198.25	$198.20
Purchase #7	$35.91	4.304%	$37.4556	$37.46	$37.45	$37.50
7 purchase totals =	$624.75		$679.7373	$679.74	$679.70	$679.80