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	$120.65	3.192%	$124.5011	$124.50	$124.50	$124.50
Purchase #2	$99.45	5.271%	$104.692	$104.69	$104.70	$104.70
Purchase #3	$149.29	10.197%	$164.5131	$164.51	$164.50	$164.50
Purchase #4	$126.61	4.667%	$132.5189	$132.52	$132.50	$132.50
Purchase #5	$156.80	9.339%	$171.4436	$171.44	$171.45	$171.40
Purchase #6	$89.61	5.293%	$94.3531	$94.35	$94.35	$94.40
Purchase #7	$71.62	11.483%	$79.8441	$79.84	$79.85	$79.80
7 purchase totals =	$814.03		$871.8659	$871.85	$871.85	$871.80