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	$92.55	6.394%	$98.4676	$98.47	$98.45	$98.50
Purchase #2	$65.43	9.211%	$71.4568	$71.46	$71.45	$71.50
Purchase #3	$196.31	7.387%	$210.8114	$210.81	$210.80	$210.80
Purchase #4	$171.32	8.200%	$185.3682	$185.37	$185.35	$185.40
Purchase #5	$152.67	8.468%	$165.5981	$165.60	$165.60	$165.60
Purchase #6	$38.47	8.508%	$41.743	$41.74	$41.75	$41.70
Purchase #7	$50.50	13.647%	$57.3917	$57.39	$57.40	$57.40
7 purchase totals =	$767.25		$830.8368	$830.84	$830.80	$830.90