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	$149.94	13.769%	$170.5852	$170.59	$170.60	$170.60
Purchase #2	$219.71	8.769%	$238.9764	$238.98	$239.00	$239.00
Purchase #3	$167.72	9.609%	$183.8362	$183.84	$183.85	$183.80
Purchase #4	$115.74	6.732%	$123.5316	$123.53	$123.55	$123.50
Purchase #5	$130.53	6.848%	$139.4687	$139.47	$139.45	$139.50
Purchase #6	$186.89	6.162%	$198.4062	$198.41	$198.40	$198.40
Purchase #7	$117.26	8.766%	$127.539	$127.54	$127.55	$127.50
7 purchase totals =	$1,087.79		$1,182.3433	$1,182.36	$1,182.40	$1,182.30