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	$38.43	6.619%	$40.9737	$40.97	$40.95	$41.00
Purchase #2	$145.47	6.486%	$154.9052	$154.91	$154.90	$154.90
Purchase #3	$42.76	10.634%	$47.3071	$47.31	$47.30	$47.30
Purchase #4	$41.70	10.136%	$45.9267	$45.93	$45.95	$45.90
Purchase #5	$199.43	8.700%	$216.7804	$216.78	$216.80	$216.80
Purchase #6	$212.69	7.320%	$228.2589	$228.26	$228.25	$228.30
Purchase #7	$33.56	11.760%	$37.5067	$37.51	$37.50	$37.50
7 purchase totals =	$714.04		$771.6587	$771.67	$771.65	$771.70