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	$33.93	10.475%	$37.4842	$37.48	$37.50	$37.50
Purchase #2	$104.56	12.242%	$117.3602	$117.36	$117.35	$117.40
Purchase #3	$216.44	5.756%	$228.8983	$228.90	$228.90	$228.90
Purchase #4	$139.79	11.122%	$155.3374	$155.34	$155.35	$155.30
Purchase #5	$92.44	12.410%	$103.9118	$103.91	$103.90	$103.90
Purchase #6	$242.50	4.262%	$252.8354	$252.84	$252.85	$252.80
Purchase #7	$250.59	6.402%	$266.6328	$266.63	$266.65	$266.60
7 purchase totals =	$1,080.25		$1,162.4601	$1,162.46	$1,162.50	$1,162.40