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	$100.88	9.652%	$110.6169	$110.62	$110.60	$110.60
Purchase #2	$79.88	4.287%	$83.3045	$83.30	$83.30	$83.30
Purchase #3	$72.70	11.691%	$81.1994	$81.20	$81.20	$81.20
Purchase #4	$232.63	10.314%	$256.6235	$256.62	$256.60	$256.60
Purchase #5	$87.76	13.428%	$99.5444	$99.54	$99.55	$99.50
Purchase #6	$200.74	4.435%	$209.6428	$209.64	$209.65	$209.60
Purchase #7	$46.35	9.727%	$50.8585	$50.86	$50.85	$50.90
7 purchase totals =	$820.94		$891.7900	$891.78	$891.75	$891.70