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	$20.66	10.544%	$22.8384	$22.84	$22.85	$22.80
Purchase #2	$89.98	3.388%	$93.0285	$93.03	$93.05	$93.00
Purchase #3	$147.94	3.214%	$152.6948	$152.69	$152.70	$152.70
Purchase #4	$100.50	6.121%	$106.6516	$106.65	$106.65	$106.70
Purchase #5	$235.59	6.211%	$250.2225	$250.22	$250.20	$250.20
Purchase #6	$105.96	5.574%	$111.8662	$111.87	$111.85	$111.90
Purchase #7	$134.57	13.403%	$152.6064	$152.61	$152.60	$152.60
7 purchase totals =	$835.20		$889.9084	$889.91	$889.90	$889.90