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	$135.36	11.418%	$150.8154	$150.82	$150.80	$150.80
Purchase #2	$54.70	5.322%	$57.6111	$57.61	$57.60	$57.60
Purchase #3	$30.97	6.662%	$33.0332	$33.03	$33.05	$33.00
Purchase #4	$179.52	10.346%	$198.0931	$198.09	$198.10	$198.10
Purchase #5	$147.69	8.751%	$160.6144	$160.61	$160.60	$160.60
Purchase #6	$105.88	12.306%	$118.9096	$118.91	$118.90	$118.90
Purchase #7	$141.78	7.665%	$152.6474	$152.65	$152.65	$152.60
7 purchase totals =	$795.90		$871.7242	$871.72	$871.70	$871.60