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	$50.99	10.555%	$56.372	$56.37	$56.35	$56.40
Purchase #2	$157.39	11.410%	$175.3482	$175.35	$175.35	$175.30
Purchase #3	$59.48	13.586%	$67.561	$67.56	$67.55	$67.60
Purchase #4	$83.49	8.404%	$90.5065	$90.51	$90.50	$90.50
Purchase #5	$59.61	11.731%	$66.6028	$66.60	$66.60	$66.60
Purchase #6	$115.60	11.616%	$129.0281	$129.03	$129.05	$129.00
Purchase #7	$195.73	10.245%	$215.7825	$215.78	$215.80	$215.80
7 purchase totals =	$722.29		$801.2011	$801.20	$801.20	$801.20