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	$136.66	10.314%	$150.7551	$150.76	$150.75	$150.80
Purchase #2	$108.27	7.851%	$116.7703	$116.77	$116.75	$116.80
Purchase #3	$19.35	5.670%	$20.4471	$20.45	$20.45	$20.40
Purchase #4	$66.69	8.116%	$72.1026	$72.10	$72.10	$72.10
Purchase #5	$83.55	9.524%	$91.5073	$91.51	$91.50	$91.50
Purchase #6	$35.56	5.827%	$37.6321	$37.63	$37.65	$37.60
Purchase #7	$54.36	5.206%	$57.19	$57.19	$57.20	$57.20
7 purchase totals =	$504.44		$546.4045	$546.41	$546.40	$546.40