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	$80.54	10.532%	$89.0225	$89.02	$89.00	$89.00
Purchase #2	$235.87	12.154%	$264.5376	$264.54	$264.55	$264.50
Purchase #3	$36.65	8.722%	$39.8466	$39.85	$39.85	$39.80
Purchase #4	$164.84	11.222%	$183.3383	$183.34	$183.35	$183.30
Purchase #5	$244.27	11.541%	$272.4612	$272.46	$272.45	$272.50
Purchase #6	$212.98	9.415%	$233.0321	$233.03	$233.05	$233.00
Purchase #7	$216.51	11.453%	$241.3069	$241.31	$241.30	$241.30
7 purchase totals =	$1,191.66		$1,323.5452	$1,323.55	$1,323.55	$1,323.40