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	$232.72	5.519%	$245.5638	$245.56	$245.55	$245.60
Purchase #2	$94.30	12.351%	$105.947	$105.95	$105.95	$105.90
Purchase #3	$200.86	11.111%	$223.1776	$223.18	$223.20	$223.20
Purchase #4	$248.88	8.795%	$270.769	$270.77	$270.75	$270.80
Purchase #5	$26.41	13.177%	$29.89	$29.89	$29.90	$29.90
Purchase #6	$45.94	12.538%	$51.7	$51.70	$51.70	$51.70
Purchase #7	$49.94	3.534%	$51.7049	$51.70	$51.70	$51.70
7 purchase totals =	$899.05		$978.7523	$978.75	$978.75	$978.80