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	$76.67	6.159%	$81.3921	$81.39	$81.40	$81.40
Purchase #2	$53.85	9.831%	$59.144	$59.14	$59.15	$59.10
Purchase #3	$161.33	6.709%	$172.1536	$172.15	$172.15	$172.20
Purchase #4	$157.82	7.299%	$169.3393	$169.34	$169.35	$169.30
Purchase #5	$132.54	10.312%	$146.2075	$146.21	$146.20	$146.20
Purchase #6	$98.65	4.173%	$102.7667	$102.77	$102.75	$102.80
Purchase #7	$237.81	11.267%	$264.6041	$264.60	$264.60	$264.60
7 purchase totals =	$918.67		$995.6073	$995.60	$995.60	$995.60