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	$143.45	12.468%	$161.3353	$161.34	$161.35	$161.30
Purchase #2	$222.55	4.863%	$233.3726	$233.37	$233.35	$233.40
Purchase #3	$39.31	7.534%	$42.2716	$42.27	$42.25	$42.30
Purchase #4	$188.31	12.567%	$211.9749	$211.97	$211.95	$212.00
Purchase #5	$174.85	5.541%	$184.5384	$184.54	$184.55	$184.50
Purchase #6	$250.96	7.649%	$270.1559	$270.16	$270.15	$270.20
Purchase #7	$166.48	13.835%	$189.5125	$189.51	$189.50	$189.50
7 purchase totals =	$1,185.91		$1,293.1612	$1,293.16	$1,293.10	$1,293.20