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	$56.55	5.160%	$59.468	$59.47	$59.45	$59.50
Purchase #2	$83.44	10.389%	$92.1086	$92.11	$92.10	$92.10
Purchase #3	$167.92	6.515%	$178.86	$178.86	$178.85	$178.90
Purchase #4	$73.35	13.526%	$83.2713	$83.27	$83.25	$83.30
Purchase #5	$154.68	7.662%	$166.5316	$166.53	$166.55	$166.50
Purchase #6	$186.38	4.184%	$194.1781	$194.18	$194.20	$194.20
Purchase #7	$206.27	5.704%	$218.0356	$218.04	$218.05	$218.00
7 purchase totals =	$928.59		$992.4532	$992.46	$992.45	$992.50