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	$38.95	8.305%	$42.1848	$42.18	$42.20	$42.20
Purchase #2	$207.94	9.138%	$226.9416	$226.94	$226.95	$226.90
Purchase #3	$17.55	3.216%	$18.1144	$18.11	$18.10	$18.10
Purchase #4	$152.67	4.726%	$159.8852	$159.89	$159.90	$159.90
Purchase #5	$12.38	10.481%	$13.6775	$13.68	$13.70	$13.70
Purchase #6	$56.41	6.168%	$59.8894	$59.89	$59.90	$59.90
Purchase #7	$245.94	7.461%	$264.2896	$264.29	$264.30	$264.30
7 purchase totals =	$731.84		$784.9825	$784.98	$785.05	$785.00