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	$121.94	4.810%	$127.8053	$127.81	$127.80	$127.80
Purchase #2	$225.26	10.524%	$248.9664	$248.97	$248.95	$249.00
Purchase #3	$199.66	3.637%	$206.9216	$206.92	$206.90	$206.90
Purchase #4	$173.67	12.809%	$195.9154	$195.92	$195.90	$195.90
Purchase #5	$151.94	10.485%	$167.8709	$167.87	$167.85	$167.90
Purchase #6	$60.73	8.322%	$65.784	$65.78	$65.80	$65.80
Purchase #7	$49.69	7.590%	$53.4615	$53.46	$53.45	$53.50
7 purchase totals =	$982.89		$1,066.7251	$1,066.73	$1,066.65	$1,066.80