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	$36.75	11.365%	$40.9266	$40.93	$40.95	$40.90
Purchase #2	$195.82	7.667%	$210.8335	$210.83	$210.85	$210.80
Purchase #3	$99.89	7.399%	$107.2809	$107.28	$107.30	$107.30
Purchase #4	$194.61	11.441%	$216.8753	$216.88	$216.90	$216.90
Purchase #5	$87.34	13.719%	$99.3222	$99.32	$99.30	$99.30
Purchase #6	$85.93	5.538%	$90.6888	$90.69	$90.70	$90.70
Purchase #7	$37.43	10.370%	$41.3115	$41.31	$41.30	$41.30
7 purchase totals =	$737.77		$807.2388	$807.24	$807.30	$807.20