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	$5.57	3.220%	$5.7494	$5.75	$5.75	$5.70
Purchase #2	$64.52	3.640%	$66.8685	$66.87	$66.85	$66.90
Purchase #3	$243.80	11.703%	$272.3319	$272.33	$272.35	$272.30
Purchase #4	$140.57	9.176%	$153.4687	$153.47	$153.45	$153.50
Purchase #5	$227.54	8.794%	$247.5499	$247.55	$247.55	$247.50
Purchase #6	$198.48	8.768%	$215.8827	$215.88	$215.90	$215.90
Purchase #7	$38.41	6.121%	$40.7611	$40.76	$40.75	$40.80
7 purchase totals =	$918.89		$1,002.6122	$1,002.61	$1,002.60	$1,002.60