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	$34.83	7.656%	$37.4966	$37.50	$37.50	$37.50
Purchase #2	$104.37	7.174%	$111.8575	$111.86	$111.85	$111.90
Purchase #3	$177.92	3.127%	$183.4836	$183.48	$183.50	$183.50
Purchase #4	$199.69	9.714%	$219.0879	$219.09	$219.10	$219.10
Purchase #5	$141.32	4.434%	$147.5861	$147.59	$147.60	$147.60
Purchase #6	$170.34	10.561%	$188.3296	$188.33	$188.35	$188.30
Purchase #7	$27.69	11.678%	$30.9236	$30.92	$30.90	$30.90
7 purchase totals =	$856.16		$918.7649	$918.77	$918.80	$918.80