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	$100.57	13.251%	$113.8965	$113.90	$113.90	$113.90
Purchase #2	$49.66	4.246%	$51.7686	$51.77	$51.75	$51.80
Purchase #3	$52.86	6.511%	$56.3017	$56.30	$56.30	$56.30
Purchase #4	$71.87	9.830%	$78.9348	$78.93	$78.95	$78.90
Purchase #5	$188.59	8.851%	$205.2821	$205.28	$205.30	$205.30
Purchase #6	$135.88	9.581%	$148.8987	$148.90	$148.90	$148.90
Purchase #7	$150.84	4.250%	$157.2507	$157.25	$157.25	$157.30
7 purchase totals =	$750.27		$812.3331	$812.33	$812.35	$812.40