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	$88.99	12.679%	$100.273	$100.27	$100.25	$100.30
Purchase #2	$111.33	12.150%	$124.8566	$124.86	$124.85	$124.90
Purchase #3	$103.89	4.463%	$108.5266	$108.53	$108.55	$108.50
Purchase #4	$77.61	7.365%	$83.326	$83.33	$83.35	$83.30
Purchase #5	$94.32	7.415%	$101.3138	$101.31	$101.30	$101.30
Purchase #6	$11.41	11.251%	$12.6937	$12.69	$12.70	$12.70
Purchase #7	$80.98	6.228%	$86.0234	$86.02	$86.00	$86.00
7 purchase totals =	$568.53		$617.0131	$617.01	$617.00	$617.00