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	$46.56	6.413%	$49.5459	$49.55	$49.55	$49.50
Purchase #2	$36.45	12.230%	$40.9078	$40.91	$40.90	$40.90
Purchase #3	$132.27	13.322%	$149.891	$149.89	$149.90	$149.90
Purchase #4	$68.78	5.738%	$72.7266	$72.73	$72.75	$72.70
Purchase #5	$95.91	5.495%	$101.1803	$101.18	$101.20	$101.20
Purchase #6	$7.78	9.696%	$8.5343	$8.53	$8.55	$8.50
Purchase #7	$133.67	11.199%	$148.6397	$148.64	$148.65	$148.60
7 purchase totals =	$521.42		$571.4256	$571.43	$571.50	$571.30