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	$64.85	9.219%	$70.8285	$70.83	$70.85	$70.80
Purchase #2	$128.85	9.556%	$141.1629	$141.16	$141.15	$141.20
Purchase #3	$37.39	11.267%	$41.6027	$41.60	$41.60	$41.60
Purchase #4	$217.25	4.306%	$226.6048	$226.60	$226.60	$226.60
Purchase #5	$72.41	11.188%	$80.5112	$80.51	$80.50	$80.50
Purchase #6	$48.91	10.446%	$54.0191	$54.02	$54.00	$54.00
Purchase #7	$138.27	13.430%	$156.8397	$156.84	$156.85	$156.80
7 purchase totals =	$707.93		$771.5689	$771.56	$771.55	$771.50