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	$235.84	6.270%	$250.6272	$250.63	$250.65	$250.60
Purchase #2	$19.98	13.807%	$22.7386	$22.74	$22.75	$22.70
Purchase #3	$228.80	11.297%	$254.6475	$254.65	$254.65	$254.60
Purchase #4	$98.78	9.161%	$107.8292	$107.83	$107.85	$107.80
Purchase #5	$158.58	8.387%	$171.8801	$171.88	$171.90	$171.90
Purchase #6	$87.79	4.499%	$91.7397	$91.74	$91.75	$91.70
Purchase #7	$189.98	3.643%	$196.901	$196.90	$196.90	$196.90
7 purchase totals =	$1,019.75		$1,096.3633	$1,096.37	$1,096.45	$1,096.20