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	$72.41	12.491%	$81.4547	$81.45	$81.45	$81.50
Purchase #2	$188.70	8.385%	$204.5225	$204.52	$204.50	$204.50
Purchase #3	$10.32	11.475%	$11.5042	$11.50	$11.50	$11.50
Purchase #4	$229.96	8.628%	$249.8009	$249.80	$249.80	$249.80
Purchase #5	$73.39	6.716%	$78.3189	$78.32	$78.30	$78.30
Purchase #6	$73.43	9.103%	$80.1143	$80.11	$80.10	$80.10
Purchase #7	$135.89	7.632%	$146.2611	$146.26	$146.25	$146.30
7 purchase totals =	$784.10		$851.9766	$851.96	$851.90	$852.00