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	$7.30	10.256%	$8.0487	$8.05	$8.05	$8.00
Purchase #2	$166.76	8.772%	$181.3882	$181.39	$181.40	$181.40
Purchase #3	$166.52	13.508%	$189.0135	$189.01	$189.00	$189.00
Purchase #4	$103.75	7.112%	$111.1287	$111.13	$111.15	$111.10
Purchase #5	$33.40	6.555%	$35.5894	$35.59	$35.60	$35.60
Purchase #6	$173.88	6.535%	$185.2431	$185.24	$185.25	$185.20
Purchase #7	$149.43	10.282%	$164.7944	$164.79	$164.80	$164.80
7 purchase totals =	$801.04		$875.2060	$875.20	$875.25	$875.10