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	$227.72	12.102%	$255.2787	$255.28	$255.30	$255.30
Purchase #2	$64.32	3.245%	$66.4072	$66.41	$66.40	$66.40
Purchase #3	$71.93	11.643%	$80.3048	$80.30	$80.30	$80.30
Purchase #4	$141.33	6.869%	$151.038	$151.04	$151.05	$151.00
Purchase #5	$39.48	6.776%	$42.1552	$42.16	$42.15	$42.20
Purchase #6	$41.64	9.288%	$45.5075	$45.51	$45.50	$45.50
Purchase #7	$23.76	4.524%	$24.8349	$24.83	$24.85	$24.80
7 purchase totals =	$610.18		$665.5263	$665.53	$665.55	$665.50