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	$235.34	13.722%	$267.6334	$267.63	$267.65	$267.60
Purchase #2	$220.27	9.165%	$240.4577	$240.46	$240.45	$240.50
Purchase #3	$43.79	5.705%	$46.2882	$46.29	$46.30	$46.30
Purchase #4	$35.66	8.312%	$38.6241	$38.62	$38.60	$38.60
Purchase #5	$55.61	3.824%	$57.7365	$57.74	$57.75	$57.70
Purchase #6	$158.43	8.780%	$172.3402	$172.34	$172.35	$172.30
Purchase #7	$109.94	6.317%	$116.8849	$116.88	$116.90	$116.90
7 purchase totals =	$859.04		$939.9650	$939.96	$940.00	$939.90