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	$24.56	13.104%	$27.7783	$27.78	$27.80	$27.80
Purchase #2	$27.40	10.301%	$30.2225	$30.22	$30.20	$30.20
Purchase #3	$162.86	4.130%	$169.5861	$169.59	$169.60	$169.60
Purchase #4	$207.80	5.415%	$219.0524	$219.05	$219.05	$219.10
Purchase #5	$142.27	3.638%	$147.4458	$147.45	$147.45	$147.40
Purchase #6	$57.98	3.339%	$59.916	$59.92	$59.90	$59.90
Purchase #7	$200.52	12.641%	$225.8677	$225.87	$225.85	$225.90
7 purchase totals =	$823.39		$879.8688	$879.88	$879.85	$879.90