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	$220.29	6.192%	$233.9304	$233.93	$233.95	$233.90
Purchase #2	$148.94	4.110%	$155.0614	$155.06	$155.05	$155.10
Purchase #3	$104.25	12.639%	$117.4262	$117.43	$117.45	$117.40
Purchase #4	$250.49	10.628%	$277.1121	$277.11	$277.10	$277.10
Purchase #5	$19.67	11.305%	$21.8937	$21.89	$21.90	$21.90
Purchase #6	$29.52	13.540%	$33.517	$33.52	$33.50	$33.50
Purchase #7	$76.61	7.802%	$82.5871	$82.59	$82.60	$82.60
7 purchase totals =	$849.77		$921.5279	$921.53	$921.55	$921.50