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	$88.37	13.515%	$100.3132	$100.31	$100.30	$100.30
Purchase #2	$96.40	4.500%	$100.738	$100.74	$100.75	$100.70
Purchase #3	$99.30	6.128%	$105.3851	$105.39	$105.40	$105.40
Purchase #4	$222.44	8.669%	$241.7233	$241.72	$241.70	$241.70
Purchase #5	$179.31	8.553%	$194.6464	$194.65	$194.65	$194.60
Purchase #6	$29.99	9.239%	$32.7608	$32.76	$32.75	$32.80
Purchase #7	$21.49	13.365%	$24.3621	$24.36	$24.35	$24.40
7 purchase totals =	$737.30		$799.9289	$799.93	$799.90	$799.90