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	$188.69	5.627%	$199.3076	$199.31	$199.30	$199.30
Purchase #2	$122.91	11.805%	$137.4195	$137.42	$137.40	$137.40
Purchase #3	$72.42	10.624%	$80.1139	$80.11	$80.10	$80.10
Purchase #4	$29.76	7.526%	$31.9997	$32.00	$32.00	$32.00
Purchase #5	$52.31	5.341%	$55.1039	$55.10	$55.10	$55.10
Purchase #6	$62.34	3.675%	$64.631	$64.63	$64.65	$64.60
Purchase #7	$92.61	6.615%	$98.7362	$98.74	$98.75	$98.70
7 purchase totals =	$621.04		$667.3118	$667.31	$667.30	$667.20