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	$156.52	6.168%	$166.1742	$166.17	$166.15	$166.20
Purchase #2	$220.71	7.152%	$236.4952	$236.50	$236.50	$236.50
Purchase #3	$237.28	3.649%	$245.9383	$245.94	$245.95	$245.90
Purchase #4	$223.63	11.851%	$250.1324	$250.13	$250.15	$250.10
Purchase #5	$113.46	7.185%	$121.6121	$121.61	$121.60	$121.60
Purchase #6	$228.69	11.663%	$255.3621	$255.36	$255.35	$255.40
Purchase #7	$111.54	5.706%	$117.9045	$117.90	$117.90	$117.90
7 purchase totals =	$1,291.83		$1,393.6188	$1,393.61	$1,393.60	$1,393.60