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	$196.36	13.445%	$222.7606	$222.76	$222.75	$222.80
Purchase #2	$195.90	9.112%	$213.7504	$213.75	$213.75	$213.80
Purchase #3	$29.50	9.380%	$32.2671	$32.27	$32.25	$32.30
Purchase #4	$128.25	13.340%	$145.3586	$145.36	$145.35	$145.40
Purchase #5	$47.41	6.860%	$50.6623	$50.66	$50.65	$50.70
Purchase #6	$113.51	3.679%	$117.686	$117.69	$117.70	$117.70
Purchase #7	$57.84	6.345%	$61.5099	$61.51	$61.50	$61.50
7 purchase totals =	$768.77		$843.9949	$844.00	$843.95	$844.20