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	$12.66	5.779%	$13.3916	$13.39	$13.40	$13.40
Purchase #2	$85.65	8.168%	$92.6459	$92.65	$92.65	$92.60
Purchase #3	$165.40	13.728%	$188.1061	$188.11	$188.10	$188.10
Purchase #4	$85.80	5.313%	$90.3586	$90.36	$90.35	$90.40
Purchase #5	$205.67	13.111%	$232.6354	$232.64	$232.65	$232.60
Purchase #6	$96.52	4.553%	$100.9146	$100.91	$100.90	$100.90
Purchase #7	$188.42	13.287%	$213.4554	$213.46	$213.45	$213.50
7 purchase totals =	$840.12		$931.5076	$931.52	$931.50	$931.50