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	$139.32	3.155%	$143.7155	$143.72	$143.70	$143.70
Purchase #2	$93.86	11.490%	$104.6445	$104.64	$104.65	$104.60
Purchase #3	$185.55	7.766%	$199.9598	$199.96	$199.95	$200.00
Purchase #4	$80.86	13.168%	$91.5076	$91.51	$91.50	$91.50
Purchase #5	$123.43	11.552%	$137.6886	$137.69	$137.70	$137.70
Purchase #6	$183.67	9.473%	$201.0691	$201.07	$201.05	$201.10
Purchase #7	$35.56	4.829%	$37.2772	$37.28	$37.30	$37.30
7 purchase totals =	$842.25		$915.8623	$915.87	$915.85	$915.90