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	$150.46	11.276%	$167.4259	$167.43	$167.45	$167.40
Purchase #2	$49.71	5.543%	$52.4654	$52.47	$52.45	$52.50
Purchase #3	$179.39	10.663%	$198.5184	$198.52	$198.50	$198.50
Purchase #4	$80.74	10.219%	$88.9908	$88.99	$89.00	$89.00
Purchase #5	$146.34	10.423%	$161.593	$161.59	$161.60	$161.60
Purchase #6	$88.40	6.866%	$94.4695	$94.47	$94.45	$94.50
Purchase #7	$142.40	6.627%	$151.8368	$151.84	$151.85	$151.80
7 purchase totals =	$837.44		$915.2998	$915.31	$915.30	$915.30