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	$78.56	4.751%	$82.2924	$82.29	$82.30	$82.30
Purchase #2	$231.57	7.823%	$249.6857	$249.69	$249.70	$249.70
Purchase #3	$35.96	5.281%	$37.859	$37.86	$37.85	$37.90
Purchase #4	$7.26	8.596%	$7.8841	$7.88	$7.90	$7.90
Purchase #5	$92.42	9.487%	$101.1879	$101.19	$101.20	$101.20
Purchase #6	$37.29	13.504%	$42.3256	$42.33	$42.35	$42.30
Purchase #7	$96.72	3.784%	$100.3799	$100.38	$100.40	$100.40
7 purchase totals =	$579.78		$621.6146	$621.62	$621.70	$621.70