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	$104.82	6.150%	$111.2664	$111.27	$111.25	$111.30
Purchase #2	$29.52	9.590%	$32.351	$32.35	$32.35	$32.40
Purchase #3	$130.82	3.237%	$135.0546	$135.05	$135.05	$135.10
Purchase #4	$153.35	7.848%	$165.3849	$165.38	$165.40	$165.40
Purchase #5	$108.47	10.199%	$119.5329	$119.53	$119.55	$119.50
Purchase #6	$225.48	8.148%	$243.8521	$243.85	$243.85	$243.90
Purchase #7	$95.61	10.292%	$105.4502	$105.45	$105.45	$105.50
7 purchase totals =	$848.07		$912.8921	$912.88	$912.90	$913.10