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	$102.83	5.334%	$108.315	$108.32	$108.30	$108.30
Purchase #2	$21.64	9.316%	$23.656	$23.66	$23.65	$23.70
Purchase #3	$85.37	5.686%	$90.2241	$90.22	$90.20	$90.20
Purchase #4	$203.57	3.590%	$210.8782	$210.88	$210.90	$210.90
Purchase #5	$57.68	3.601%	$59.7571	$59.76	$59.75	$59.80
Purchase #6	$242.82	9.131%	$264.9919	$264.99	$265.00	$265.00
Purchase #7	$172.66	4.585%	$180.5765	$180.58	$180.60	$180.60
7 purchase totals =	$886.57		$938.3988	$938.41	$938.40	$938.50