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	$159.71	12.400%	$179.514	$179.51	$179.50	$179.50
Purchase #2	$41.43	10.637%	$45.8369	$45.84	$45.85	$45.80
Purchase #3	$240.61	12.356%	$270.3398	$270.34	$270.35	$270.30
Purchase #4	$98.92	13.535%	$112.3088	$112.31	$112.30	$112.30
Purchase #5	$143.30	8.227%	$155.0893	$155.09	$155.10	$155.10
Purchase #6	$10.37	3.863%	$10.7706	$10.77	$10.75	$10.80
Purchase #7	$134.40	8.859%	$146.3065	$146.31	$146.30	$146.30
7 purchase totals =	$828.74		$920.1659	$920.17	$920.15	$920.10