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	$232.34	4.573%	$242.9649	$242.96	$242.95	$243.00
Purchase #2	$126.27	13.152%	$142.877	$142.88	$142.90	$142.90
Purchase #3	$65.45	10.765%	$72.4957	$72.50	$72.50	$72.50
Purchase #4	$15.91	9.359%	$17.399	$17.40	$17.40	$17.40
Purchase #5	$69.65	7.360%	$74.7762	$74.78	$74.80	$74.80
Purchase #6	$130.54	10.845%	$144.6971	$144.70	$144.70	$144.70
Purchase #7	$45.91	10.767%	$50.8531	$50.85	$50.85	$50.90
7 purchase totals =	$686.07		$746.0630	$746.07	$746.10	$746.20