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	$101.88	7.407%	$109.4263	$109.43	$109.45	$109.40
Purchase #2	$73.90	6.692%	$78.8454	$78.85	$78.85	$78.80
Purchase #3	$137.87	6.136%	$146.3297	$146.33	$146.35	$146.30
Purchase #4	$244.94	13.308%	$277.5366	$277.54	$277.55	$277.50
Purchase #5	$66.77	8.246%	$72.2759	$72.28	$72.30	$72.30
Purchase #6	$80.32	6.354%	$85.4235	$85.42	$85.40	$85.40
Purchase #7	$37.98	9.290%	$41.5083	$41.51	$41.50	$41.50
7 purchase totals =	$743.66		$811.3457	$811.36	$811.40	$811.20