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	$200.51	7.774%	$216.0976	$216.10	$216.10	$216.10
Purchase #2	$131.66	13.653%	$149.6355	$149.64	$149.65	$149.60
Purchase #3	$30.83	4.635%	$32.259	$32.26	$32.25	$32.30
Purchase #4	$66.88	7.339%	$71.7883	$71.79	$71.80	$71.80
Purchase #5	$82.60	11.386%	$92.0048	$92.00	$92.00	$92.00
Purchase #6	$34.81	8.157%	$37.6495	$37.65	$37.65	$37.60
Purchase #7	$63.49	3.768%	$65.8823	$65.88	$65.90	$65.90
7 purchase totals =	$610.78		$665.3170	$665.32	$665.35	$665.30