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	$246.60	7.577%	$265.2849	$265.28	$265.30	$265.30
Purchase #2	$136.41	11.295%	$151.8175	$151.82	$151.80	$151.80
Purchase #3	$180.69	8.760%	$196.5184	$196.52	$196.50	$196.50
Purchase #4	$74.64	8.665%	$81.1076	$81.11	$81.10	$81.10
Purchase #5	$122.28	7.417%	$131.3495	$131.35	$131.35	$131.30
Purchase #6	$40.51	8.287%	$43.8671	$43.87	$43.85	$43.90
Purchase #7	$149.81	13.565%	$170.1317	$170.13	$170.15	$170.10
7 purchase totals =	$950.94		$1,040.0767	$1,040.08	$1,040.05	$1,040.00