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	$248.85	10.790%	$275.7009	$275.70	$275.70	$275.70
Purchase #2	$201.91	7.116%	$216.2779	$216.28	$216.30	$216.30
Purchase #3	$221.97	12.528%	$249.7784	$249.78	$249.80	$249.80
Purchase #4	$27.94	12.609%	$31.463	$31.46	$31.45	$31.50
Purchase #5	$218.69	9.228%	$238.8707	$238.87	$238.85	$238.90
Purchase #6	$65.45	10.269%	$72.1711	$72.17	$72.15	$72.20
Purchase #7	$207.28	7.384%	$222.5856	$222.59	$222.60	$222.60
7 purchase totals =	$1,192.09		$1,306.8476	$1,306.85	$1,306.85	$1,307.00