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	$246.84	12.653%	$278.0727	$278.07	$278.05	$278.10
Purchase #2	$223.34	9.579%	$244.7337	$244.73	$244.75	$244.70
Purchase #3	$127.88	12.225%	$143.5133	$143.51	$143.50	$143.50
Purchase #4	$23.90	3.474%	$24.7303	$24.73	$24.75	$24.70
Purchase #5	$173.59	10.253%	$191.3882	$191.39	$191.40	$191.40
Purchase #6	$167.56	10.750%	$185.5727	$185.57	$185.55	$185.60
Purchase #7	$38.25	10.409%	$42.2314	$42.23	$42.25	$42.20
7 purchase totals =	$1,001.36		$1,110.2423	$1,110.23	$1,110.25	$1,110.20