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	$79.80	5.546%	$84.2257	$84.23	$84.25	$84.20
Purchase #2	$85.69	5.243%	$90.1827	$90.18	$90.20	$90.20
Purchase #3	$82.85	10.482%	$91.5343	$91.53	$91.55	$91.50
Purchase #4	$109.88	13.284%	$124.4765	$124.48	$124.50	$124.50
Purchase #5	$117.38	11.150%	$130.4679	$130.47	$130.45	$130.50
Purchase #6	$55.47	8.657%	$60.272	$60.27	$60.25	$60.30
Purchase #7	$31.35	5.564%	$33.0943	$33.09	$33.10	$33.10
7 purchase totals =	$562.42		$614.2534	$614.25	$614.30	$614.30