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	$135.50	10.822%	$150.1638	$150.16	$150.15	$150.20
Purchase #2	$34.39	9.488%	$37.6529	$37.65	$37.65	$37.70
Purchase #3	$101.57	9.829%	$111.5533	$111.55	$111.55	$111.60
Purchase #4	$96.33	8.270%	$104.2965	$104.30	$104.30	$104.30
Purchase #5	$35.46	11.501%	$39.5383	$39.54	$39.55	$39.50
Purchase #6	$160.33	7.314%	$172.0565	$172.06	$172.05	$172.10
Purchase #7	$208.67	10.707%	$231.0123	$231.01	$231.00	$231.00
7 purchase totals =	$772.25		$846.2736	$846.27	$846.25	$846.40