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	$38.36	10.334%	$42.3241	$42.32	$42.30	$42.30
Purchase #2	$69.34	11.510%	$77.321	$77.32	$77.30	$77.30
Purchase #3	$150.90	12.434%	$169.6629	$169.66	$169.65	$169.70
Purchase #4	$36.75	4.653%	$38.46	$38.46	$38.45	$38.50
Purchase #5	$56.46	5.339%	$59.4744	$59.47	$59.45	$59.50
Purchase #6	$100.65	8.697%	$109.4035	$109.40	$109.40	$109.40
Purchase #7	$91.72	11.450%	$102.2219	$102.22	$102.20	$102.20
7 purchase totals =	$544.18		$598.8678	$598.85	$598.75	$598.90