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	$90.32	10.192%	$99.5254	$99.53	$99.55	$99.50
Purchase #2	$43.29	4.839%	$45.3848	$45.38	$45.40	$45.40
Purchase #3	$8.42	10.337%	$9.2904	$9.29	$9.30	$9.30
Purchase #4	$172.77	9.747%	$189.6099	$189.61	$189.60	$189.60
Purchase #5	$63.38	3.668%	$65.7048	$65.70	$65.70	$65.70
Purchase #6	$107.62	5.710%	$113.7651	$113.77	$113.75	$113.80
Purchase #7	$55.40	5.702%	$58.5589	$58.56	$58.55	$58.60
7 purchase totals =	$541.20		$581.8393	$581.84	$581.85	$581.90