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	$134.44	12.694%	$151.5058	$151.51	$151.50	$151.50
Purchase #2	$40.56	5.562%	$42.8159	$42.82	$42.80	$42.80
Purchase #3	$73.60	9.119%	$80.3116	$80.31	$80.30	$80.30
Purchase #4	$98.93	5.164%	$104.0387	$104.04	$104.05	$104.00
Purchase #5	$250.98	5.348%	$264.4024	$264.40	$264.40	$264.40
Purchase #6	$48.52	4.583%	$50.7437	$50.74	$50.75	$50.70
Purchase #7	$139.96	13.320%	$158.6027	$158.60	$158.60	$158.60
7 purchase totals =	$786.99		$852.4208	$852.42	$852.40	$852.30