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	$27.62	4.273%	$28.8002	$28.80	$28.80	$28.80
Purchase #2	$192.83	12.260%	$216.471	$216.47	$216.45	$216.50
Purchase #3	$140.61	6.796%	$150.1659	$150.17	$150.15	$150.20
Purchase #4	$47.50	4.163%	$49.4774	$49.48	$49.50	$49.50
Purchase #5	$247.94	5.461%	$261.48	$261.48	$261.50	$261.50
Purchase #6	$100.53	4.827%	$105.3826	$105.38	$105.40	$105.40
Purchase #7	$93.86	8.770%	$102.0915	$102.09	$102.10	$102.10
7 purchase totals =	$850.89		$913.8686	$913.87	$913.90	$914.00