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	$55.73	8.503%	$60.4687	$60.47	$60.45	$60.50
Purchase #2	$82.70	10.820%	$91.6481	$91.65	$91.65	$91.60
Purchase #3	$174.30	8.800%	$189.6384	$189.64	$189.65	$189.60
Purchase #4	$110.69	11.420%	$123.3308	$123.33	$123.35	$123.30
Purchase #5	$27.71	7.290%	$29.7301	$29.73	$29.75	$29.70
Purchase #6	$125.81	5.304%	$132.483	$132.48	$132.50	$132.50
Purchase #7	$205.30	13.617%	$233.2557	$233.26	$233.25	$233.30
7 purchase totals =	$782.24		$860.5548	$860.56	$860.60	$860.50