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	$81.49	4.550%	$85.1978	$85.20	$85.20	$85.20
Purchase #2	$246.65	7.488%	$265.1192	$265.12	$265.10	$265.10
Purchase #3	$117.49	5.681%	$124.1646	$124.16	$124.15	$124.20
Purchase #4	$245.31	7.450%	$263.5856	$263.59	$263.60	$263.60
Purchase #5	$183.90	8.446%	$199.4322	$199.43	$199.45	$199.40
Purchase #6	$37.76	6.167%	$40.0887	$40.09	$40.10	$40.10
Purchase #7	$120.42	9.147%	$131.4348	$131.43	$131.45	$131.40
7 purchase totals =	$1,033.02		$1,109.0229	$1,109.02	$1,109.05	$1,109.00