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	$70.42	11.357%	$78.4176	$78.42	$78.40	$78.40
Purchase #2	$59.96	4.416%	$62.6078	$62.61	$62.60	$62.60
Purchase #3	$212.31	10.747%	$235.127	$235.13	$235.15	$235.10
Purchase #4	$144.71	8.387%	$156.8468	$156.85	$156.85	$156.80
Purchase #5	$202.79	5.120%	$213.1728	$213.17	$213.15	$213.20
Purchase #6	$161.63	6.484%	$172.1101	$172.11	$172.10	$172.10
Purchase #7	$213.33	12.437%	$239.8619	$239.86	$239.85	$239.90
7 purchase totals =	$1,065.15		$1,158.1440	$1,158.15	$1,158.10	$1,158.10