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	$134.46	3.830%	$139.6098	$139.61	$139.60	$139.60
Purchase #2	$118.32	3.642%	$122.6292	$122.63	$122.65	$122.60
Purchase #3	$191.90	4.589%	$200.7063	$200.71	$200.70	$200.70
Purchase #4	$228.67	5.757%	$241.8345	$241.83	$241.85	$241.80
Purchase #5	$31.31	12.729%	$35.2954	$35.30	$35.30	$35.30
Purchase #6	$171.63	8.409%	$186.0624	$186.06	$186.05	$186.10
Purchase #7	$168.95	9.575%	$185.127	$185.13	$185.15	$185.10
7 purchase totals =	$1,045.24		$1,111.2646	$1,111.27	$1,111.30	$1,111.20