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	$200.53	11.362%	$223.3142	$223.31	$223.30	$223.30
Purchase #2	$144.51	13.867%	$164.5492	$164.55	$164.55	$164.50
Purchase #3	$83.82	13.661%	$95.2707	$95.27	$95.25	$95.30
Purchase #4	$224.66	10.399%	$248.0224	$248.02	$248.00	$248.00
Purchase #5	$240.48	4.304%	$250.8303	$250.83	$250.85	$250.80
Purchase #6	$184.75	10.497%	$204.1432	$204.14	$204.15	$204.10
Purchase #7	$94.38	9.448%	$103.297	$103.30	$103.30	$103.30
7 purchase totals =	$1,173.13		$1,289.4270	$1,289.42	$1,289.40	$1,289.30