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	$80.96	3.132%	$83.4957	$83.50	$83.50	$83.50
Purchase #2	$220.52	11.124%	$245.0506	$245.05	$245.05	$245.10
Purchase #3	$15.97	3.696%	$16.5603	$16.56	$16.55	$16.60
Purchase #4	$45.28	11.451%	$50.465	$50.47	$50.45	$50.50
Purchase #5	$238.98	7.504%	$256.9131	$256.91	$256.90	$256.90
Purchase #6	$90.34	5.206%	$95.0431	$95.04	$95.05	$95.00
Purchase #7	$55.69	6.225%	$59.1567	$59.16	$59.15	$59.20
7 purchase totals =	$747.74		$806.6845	$806.69	$806.65	$806.80