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	$127.57	9.419%	$139.5858	$139.59	$139.60	$139.60
Purchase #2	$60.55	7.809%	$65.2783	$65.28	$65.30	$65.30
Purchase #3	$220.91	7.576%	$237.6461	$237.65	$237.65	$237.60
Purchase #4	$169.56	10.431%	$187.2468	$187.25	$187.25	$187.20
Purchase #5	$50.54	13.496%	$57.3609	$57.36	$57.35	$57.40
Purchase #6	$79.85	4.674%	$83.5822	$83.58	$83.60	$83.60
Purchase #7	$35.53	5.852%	$37.6092	$37.61	$37.60	$37.60
7 purchase totals =	$744.51		$808.3093	$808.32	$808.35	$808.30