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	$150.99	13.457%	$171.3087	$171.31	$171.30	$171.30
Purchase #2	$121.52	9.121%	$132.6038	$132.60	$132.60	$132.60
Purchase #3	$131.78	12.168%	$147.815	$147.82	$147.80	$147.80
Purchase #4	$135.76	3.136%	$140.0174	$140.02	$140.00	$140.00
Purchase #5	$80.91	10.219%	$89.1782	$89.18	$89.20	$89.20
Purchase #6	$195.61	12.177%	$219.4294	$219.43	$219.45	$219.40
Purchase #7	$35.55	13.244%	$40.2582	$40.26	$40.25	$40.30
7 purchase totals =	$852.12		$940.6107	$940.62	$940.60	$940.60