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	$112.89	9.325%	$123.417	$123.42	$123.40	$123.40
Purchase #2	$176.46	8.653%	$191.7291	$191.73	$191.75	$191.70
Purchase #3	$9.55	8.104%	$10.3239	$10.32	$10.30	$10.30
Purchase #4	$134.56	10.564%	$148.7749	$148.77	$148.75	$148.80
Purchase #5	$149.57	11.365%	$166.5686	$166.57	$166.55	$166.60
Purchase #6	$36.77	9.852%	$40.3926	$40.39	$40.40	$40.40
Purchase #7	$169.86	6.626%	$181.1149	$181.11	$181.10	$181.10
7 purchase totals =	$789.66		$862.3210	$862.31	$862.25	$862.30