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	$209.45	3.359%	$216.4854	$216.49	$216.50	$216.50
Purchase #2	$247.25	7.680%	$266.2388	$266.24	$266.25	$266.20
Purchase #3	$38.34	4.722%	$40.1504	$40.15	$40.15	$40.20
Purchase #4	$113.44	6.268%	$120.5504	$120.55	$120.55	$120.60
Purchase #5	$29.97	3.790%	$31.1059	$31.11	$31.10	$31.10
Purchase #6	$141.88	12.292%	$159.3199	$159.32	$159.30	$159.30
Purchase #7	$160.53	3.692%	$166.4568	$166.46	$166.45	$166.50
7 purchase totals =	$940.86		$1,000.3076	$1,000.32	$1,000.30	$1,000.40