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	$35.59	6.145%	$37.777	$37.78	$37.80	$37.80
Purchase #2	$192.53	4.294%	$200.7972	$200.80	$200.80	$200.80
Purchase #3	$159.47	5.199%	$167.7608	$167.76	$167.75	$167.80
Purchase #4	$165.61	13.812%	$188.4841	$188.48	$188.50	$188.50
Purchase #5	$86.65	11.409%	$96.5359	$96.54	$96.55	$96.50
Purchase #6	$97.99	6.125%	$103.9919	$103.99	$104.00	$104.00
Purchase #7	$54.56	9.210%	$59.585	$59.59	$59.60	$59.60
7 purchase totals =	$792.40		$854.9319	$854.94	$855.00	$855.00