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	$153.36	3.559%	$158.8181	$158.82	$158.80	$158.80
Purchase #2	$115.74	5.431%	$122.0258	$122.03	$122.05	$122.00
Purchase #3	$211.31	7.612%	$227.3949	$227.39	$227.40	$227.40
Purchase #4	$139.90	6.435%	$148.9026	$148.90	$148.90	$148.90
Purchase #5	$40.80	3.690%	$42.3055	$42.31	$42.30	$42.30
Purchase #6	$89.86	6.697%	$95.8779	$95.88	$95.90	$95.90
Purchase #7	$156.86	11.160%	$174.3656	$174.37	$174.35	$174.40
7 purchase totals =	$907.83		$969.6904	$969.70	$969.70	$969.70