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	$73.79	10.298%	$81.3889	$81.39	$81.40	$81.40
Purchase #2	$144.51	7.694%	$155.6286	$155.63	$155.65	$155.60
Purchase #3	$48.87	13.643%	$55.5373	$55.54	$55.55	$55.50
Purchase #4	$234.50	9.789%	$257.4552	$257.46	$257.45	$257.50
Purchase #5	$55.80	11.668%	$62.3107	$62.31	$62.30	$62.30
Purchase #6	$33.91	11.769%	$37.9009	$37.90	$37.90	$37.90
Purchase #7	$200.67	5.729%	$212.1664	$212.17	$212.15	$212.20
7 purchase totals =	$792.05		$862.3880	$862.40	$862.40	$862.40