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	$171.73	8.471%	$186.2772	$186.28	$186.30	$186.30
Purchase #2	$243.47	13.558%	$276.4797	$276.48	$276.50	$276.50
Purchase #3	$70.40	11.748%	$78.6706	$78.67	$78.65	$78.70
Purchase #4	$244.34	4.663%	$255.7336	$255.73	$255.75	$255.70
Purchase #5	$97.50	12.703%	$109.8854	$109.89	$109.90	$109.90
Purchase #6	$189.45	8.699%	$205.9303	$205.93	$205.95	$205.90
Purchase #7	$122.67	6.333%	$130.4387	$130.44	$130.45	$130.40
7 purchase totals =	$1,139.56		$1,243.4155	$1,243.42	$1,243.50	$1,243.40