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	$250.89	9.129%	$273.7937	$273.79	$273.80	$273.80
Purchase #2	$75.59	3.103%	$77.9356	$77.94	$77.95	$77.90
Purchase #3	$146.68	13.455%	$166.4158	$166.42	$166.40	$166.40
Purchase #4	$60.63	4.349%	$63.2668	$63.27	$63.25	$63.30
Purchase #5	$103.49	4.751%	$108.4068	$108.41	$108.40	$108.40
Purchase #6	$187.45	4.796%	$196.4401	$196.44	$196.45	$196.40
Purchase #7	$115.48	4.683%	$120.8879	$120.89	$120.90	$120.90
7 purchase totals =	$940.21		$1,007.1467	$1,007.16	$1,007.15	$1,007.10