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	$24.57	10.537%	$27.1589	$27.16	$27.15	$27.20
Purchase #2	$172.44	7.771%	$185.8403	$185.84	$185.85	$185.80
Purchase #3	$215.49	4.314%	$224.7862	$224.79	$224.80	$224.80
Purchase #4	$64.82	8.854%	$70.5592	$70.56	$70.55	$70.60
Purchase #5	$49.28	8.688%	$53.5614	$53.56	$53.55	$53.60
Purchase #6	$96.49	3.315%	$99.6886	$99.69	$99.70	$99.70
Purchase #7	$160.38	4.713%	$167.9387	$167.94	$167.95	$167.90
7 purchase totals =	$783.47		$829.5333	$829.54	$829.55	$829.60