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	$55.34	13.865%	$63.0129	$63.01	$63.00	$63.00
Purchase #2	$203.82	9.358%	$222.8935	$222.89	$222.90	$222.90
Purchase #3	$95.45	3.793%	$99.0704	$99.07	$99.05	$99.10
Purchase #4	$156.28	12.258%	$175.4368	$175.44	$175.45	$175.40
Purchase #5	$93.98	12.243%	$105.486	$105.49	$105.50	$105.50
Purchase #6	$223.65	10.854%	$247.925	$247.93	$247.95	$247.90
Purchase #7	$79.53	7.425%	$85.4351	$85.44	$85.45	$85.40
7 purchase totals =	$908.05		$999.2597	$999.27	$999.30	$999.20