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	$137.96	12.337%	$154.9801	$154.98	$155.00	$155.00
Purchase #2	$221.83	5.815%	$234.7294	$234.73	$234.75	$234.70
Purchase #3	$227.38	8.122%	$245.8478	$245.85	$245.85	$245.80
Purchase #4	$84.89	6.103%	$90.0708	$90.07	$90.05	$90.10
Purchase #5	$171.34	4.784%	$179.5369	$179.54	$179.55	$179.50
Purchase #6	$175.32	12.324%	$196.9264	$196.93	$196.95	$196.90
Purchase #7	$81.70	12.832%	$92.1837	$92.18	$92.20	$92.20
7 purchase totals =	$1,100.42		$1,194.2751	$1,194.28	$1,194.35	$1,194.20