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	$9.67	8.397%	$10.482	$10.48	$10.50	$10.50
Purchase #2	$89.89	3.194%	$92.7611	$92.76	$92.75	$92.80
Purchase #3	$16.61	3.526%	$17.1957	$17.20	$17.20	$17.20
Purchase #4	$124.78	4.549%	$130.4562	$130.46	$130.45	$130.50
Purchase #5	$237.67	9.186%	$259.5024	$259.50	$259.50	$259.50
Purchase #6	$69.27	5.276%	$72.9247	$72.92	$72.90	$72.90
Purchase #7	$67.70	6.682%	$72.2237	$72.22	$72.20	$72.20
7 purchase totals =	$615.59		$655.5458	$655.54	$655.50	$655.60