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	$92.88	7.239%	$99.6036	$99.60	$99.60	$99.60
Purchase #2	$84.49	3.129%	$87.1337	$87.13	$87.15	$87.10
Purchase #3	$54.77	9.154%	$59.7836	$59.78	$59.80	$59.80
Purchase #4	$211.69	9.511%	$231.8238	$231.82	$231.80	$231.80
Purchase #5	$175.52	8.498%	$190.4357	$190.44	$190.45	$190.40
Purchase #6	$244.74	5.170%	$257.3931	$257.39	$257.40	$257.40
Purchase #7	$242.73	12.833%	$273.8795	$273.88	$273.90	$273.90
7 purchase totals =	$1,106.82		$1,200.0530	$1,200.04	$1,200.10	$1,200.00