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	$28.34	10.865%	$31.4191	$31.42	$31.40	$31.40
Purchase #2	$108.46	7.697%	$116.8082	$116.81	$116.80	$116.80
Purchase #3	$77.90	10.178%	$85.8287	$85.83	$85.85	$85.80
Purchase #4	$87.61	4.717%	$91.7426	$91.74	$91.75	$91.70
Purchase #5	$58.98	13.303%	$66.8261	$66.83	$66.85	$66.80
Purchase #6	$237.46	6.672%	$253.3033	$253.30	$253.30	$253.30
Purchase #7	$147.86	11.407%	$164.7264	$164.73	$164.75	$164.70
7 purchase totals =	$746.61		$810.6544	$810.66	$810.70	$810.50