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	$92.50	6.363%	$98.3858	$98.39	$98.40	$98.40
Purchase #2	$22.68	13.341%	$25.7057	$25.71	$25.70	$25.70
Purchase #3	$238.36	3.589%	$246.9147	$246.91	$246.90	$246.90
Purchase #4	$55.72	12.720%	$62.8076	$62.81	$62.80	$62.80
Purchase #5	$94.82	5.820%	$100.3385	$100.34	$100.35	$100.30
Purchase #6	$115.36	12.695%	$130.005	$130.01	$130.00	$130.00
Purchase #7	$124.36	5.679%	$131.4224	$131.42	$131.40	$131.40
7 purchase totals =	$743.80		$795.5797	$795.59	$795.55	$795.50