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	$200.37	9.585%	$219.5755	$219.58	$219.60	$219.60
Purchase #2	$241.41	3.667%	$250.2625	$250.26	$250.25	$250.30
Purchase #3	$166.76	13.692%	$189.5928	$189.59	$189.60	$189.60
Purchase #4	$68.89	3.780%	$71.494	$71.49	$71.50	$71.50
Purchase #5	$6.56	4.719%	$6.8696	$6.87	$6.85	$6.90
Purchase #6	$250.48	5.661%	$264.6597	$264.66	$264.65	$264.70
Purchase #7	$69.69	13.776%	$79.2905	$79.29	$79.30	$79.30
7 purchase totals =	$1,004.16		$1,081.7446	$1,081.74	$1,081.75	$1,081.90