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	$236.52	11.792%	$264.4104	$264.41	$264.40	$264.40
Purchase #2	$33.79	11.749%	$37.76	$37.76	$37.75	$37.80
Purchase #3	$48.98	3.282%	$50.5875	$50.59	$50.60	$50.60
Purchase #4	$131.74	6.476%	$140.2715	$140.27	$140.25	$140.30
Purchase #5	$52.29	8.730%	$56.8549	$56.85	$56.85	$56.90
Purchase #6	$23.96	10.797%	$26.547	$26.55	$26.55	$26.50
Purchase #7	$77.46	4.209%	$80.7203	$80.72	$80.70	$80.70
7 purchase totals =	$604.74		$657.1516	$657.15	$657.10	$657.20