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	$78.93	12.149%	$88.5192	$88.52	$88.50	$88.50
Purchase #2	$131.92	13.155%	$149.2741	$149.27	$149.25	$149.30
Purchase #3	$241.63	7.149%	$258.9041	$258.90	$258.90	$258.90
Purchase #4	$59.34	5.526%	$62.6191	$62.62	$62.60	$62.60
Purchase #5	$175.64	13.742%	$199.7764	$199.78	$199.80	$199.80
Purchase #6	$52.32	4.785%	$54.8235	$54.82	$54.80	$54.80
Purchase #7	$192.31	12.714%	$216.7603	$216.76	$216.75	$216.80
7 purchase totals =	$932.09		$1,030.6767	$1,030.67	$1,030.60	$1,030.70