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	$25.87	13.277%	$29.3048	$29.30	$29.30	$29.30
Purchase #2	$176.86	11.183%	$196.6383	$196.64	$196.65	$196.60
Purchase #3	$102.69	5.401%	$108.2363	$108.24	$108.25	$108.20
Purchase #4	$63.71	3.279%	$65.7991	$65.80	$65.80	$65.80
Purchase #5	$225.47	7.626%	$242.6643	$242.66	$242.65	$242.70
Purchase #6	$80.52	12.417%	$90.5182	$90.52	$90.50	$90.50
Purchase #7	$26.40	8.865%	$28.7404	$28.74	$28.75	$28.70
7 purchase totals =	$701.52		$761.9014	$761.90	$761.90	$761.80