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	$28.89	13.173%	$32.6957	$32.70	$32.70	$32.70
Purchase #2	$145.43	13.485%	$165.0412	$165.04	$165.05	$165.00
Purchase #3	$117.89	11.782%	$131.7798	$131.78	$131.80	$131.80
Purchase #4	$103.36	9.862%	$113.5534	$113.55	$113.55	$113.60
Purchase #5	$31.83	11.399%	$35.4583	$35.46	$35.45	$35.50
Purchase #6	$100.84	13.494%	$114.4473	$114.45	$114.45	$114.40
Purchase #7	$172.40	4.800%	$180.6752	$180.68	$180.70	$180.70
7 purchase totals =	$700.64		$773.6509	$773.66	$773.70	$773.70