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	$96.79	12.468%	$108.8578	$108.86	$108.85	$108.90
Purchase #2	$182.56	9.432%	$199.7791	$199.78	$199.80	$199.80
Purchase #3	$80.47	11.513%	$89.7345	$89.73	$89.75	$89.70
Purchase #4	$229.70	5.505%	$242.345	$242.35	$242.35	$242.30
Purchase #5	$70.42	3.302%	$72.7453	$72.75	$72.75	$72.70
Purchase #6	$245.81	10.590%	$271.8413	$271.84	$271.85	$271.80
Purchase #7	$176.77	12.616%	$199.0713	$199.07	$199.05	$199.10
7 purchase totals =	$1,082.52		$1,184.3743	$1,184.38	$1,184.40	$1,184.30