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	$48.83	8.557%	$53.0084	$53.01	$53.00	$53.00
Purchase #2	$43.54	4.320%	$45.4209	$45.42	$45.40	$45.40
Purchase #3	$156.88	10.147%	$172.7986	$172.80	$172.80	$172.80
Purchase #4	$105.62	4.187%	$110.0423	$110.04	$110.05	$110.00
Purchase #5	$220.56	9.564%	$241.6544	$241.65	$241.65	$241.70
Purchase #6	$140.89	5.459%	$148.5812	$148.58	$148.60	$148.60
Purchase #7	$135.81	10.745%	$150.4028	$150.40	$150.40	$150.40
7 purchase totals =	$852.13		$921.9086	$921.90	$921.90	$921.90