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	$80.58	10.548%	$89.0796	$89.08	$89.10	$89.10
Purchase #2	$68.55	5.768%	$72.504	$72.50	$72.50	$72.50
Purchase #3	$157.63	9.513%	$172.6253	$172.63	$172.65	$172.60
Purchase #4	$66.60	10.358%	$73.4984	$73.50	$73.50	$73.50
Purchase #5	$240.45	12.597%	$270.7395	$270.74	$270.75	$270.70
Purchase #6	$147.98	6.475%	$157.5617	$157.56	$157.55	$157.60
Purchase #7	$216.55	12.599%	$243.8331	$243.83	$243.85	$243.80
7 purchase totals =	$978.34		$1,079.8416	$1,079.84	$1,079.90	$1,079.80