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	$41.55	3.342%	$42.9386	$42.94	$42.95	$42.90
Purchase #2	$65.56	12.613%	$73.8291	$73.83	$73.85	$73.80
Purchase #3	$38.97	10.512%	$43.0665	$43.07	$43.05	$43.10
Purchase #4	$91.72	7.776%	$98.8521	$98.85	$98.85	$98.90
Purchase #5	$178.73	4.395%	$186.5852	$186.59	$186.60	$186.60
Purchase #6	$191.81	11.500%	$213.8682	$213.87	$213.85	$213.90
Purchase #7	$75.61	11.104%	$84.0057	$84.01	$84.00	$84.00
7 purchase totals =	$683.95		$743.1454	$743.16	$743.15	$743.20