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	$44.30	10.331%	$48.8766	$48.88	$48.90	$48.90
Purchase #2	$136.78	9.863%	$150.2706	$150.27	$150.25	$150.30
Purchase #3	$63.81	11.696%	$71.2732	$71.27	$71.25	$71.30
Purchase #4	$198.83	10.536%	$219.7787	$219.78	$219.80	$219.80
Purchase #5	$54.53	3.534%	$56.4571	$56.46	$56.45	$56.50
Purchase #6	$96.45	7.639%	$103.8178	$103.82	$103.80	$103.80
Purchase #7	$6.37	12.754%	$7.1824	$7.18	$7.20	$7.20
7 purchase totals =	$601.07		$657.6564	$657.66	$657.65	$657.80