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	$28.42	6.423%	$30.2454	$30.25	$30.25	$30.20
Purchase #2	$40.25	3.758%	$41.7626	$41.76	$41.75	$41.80
Purchase #3	$83.28	8.446%	$90.3138	$90.31	$90.30	$90.30
Purchase #4	$222.69	10.833%	$246.814	$246.81	$246.80	$246.80
Purchase #5	$208.79	6.763%	$222.9105	$222.91	$222.90	$222.90
Purchase #6	$190.63	4.198%	$198.6326	$198.63	$198.65	$198.60
Purchase #7	$92.35	12.437%	$103.8356	$103.84	$103.85	$103.80
7 purchase totals =	$866.41		$934.5145	$934.51	$934.50	$934.40