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	$35.77	5.870%	$37.8697	$37.87	$37.85	$37.90
Purchase #2	$206.78	9.135%	$225.6694	$225.67	$225.65	$225.70
Purchase #3	$88.34	12.643%	$99.5088	$99.51	$99.50	$99.50
Purchase #4	$236.86	13.360%	$268.5045	$268.50	$268.50	$268.50
Purchase #5	$220.62	8.304%	$238.9403	$238.94	$238.95	$238.90
Purchase #6	$98.57	10.415%	$108.8361	$108.84	$108.85	$108.80
Purchase #7	$26.30	9.716%	$28.8553	$28.86	$28.85	$28.90
7 purchase totals =	$913.24		$1,008.1841	$1,008.19	$1,008.15	$1,008.20