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	$83.93	7.581%	$90.2927	$90.29	$90.30	$90.30
Purchase #2	$81.67	11.284%	$90.8856	$90.89	$90.90	$90.90
Purchase #3	$139.32	5.264%	$146.6538	$146.65	$146.65	$146.70
Purchase #4	$175.95	10.133%	$193.779	$193.78	$193.80	$193.80
Purchase #5	$103.99	9.328%	$113.6902	$113.69	$113.70	$113.70
Purchase #6	$35.31	11.269%	$39.2891	$39.29	$39.30	$39.30
Purchase #7	$245.78	4.392%	$256.5747	$256.57	$256.55	$256.60
7 purchase totals =	$865.95		$931.1651	$931.16	$931.20	$931.30