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	$50.92	13.467%	$57.7774	$57.78	$57.80	$57.80
Purchase #2	$200.71	4.574%	$209.8905	$209.89	$209.90	$209.90
Purchase #3	$165.86	13.833%	$188.8034	$188.80	$188.80	$188.80
Purchase #4	$99.83	6.791%	$106.6095	$106.61	$106.60	$106.60
Purchase #5	$113.47	3.647%	$117.6083	$117.61	$117.60	$117.60
Purchase #6	$86.91	3.643%	$90.0761	$90.08	$90.10	$90.10
Purchase #7	$19.86	4.593%	$20.7722	$20.77	$20.75	$20.80
7 purchase totals =	$737.56		$791.5374	$791.54	$791.55	$791.60