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	$52.92	8.183%	$57.2504	$57.25	$57.25	$57.30
Purchase #2	$183.41	4.441%	$191.5552	$191.56	$191.55	$191.60
Purchase #3	$105.40	6.805%	$112.5725	$112.57	$112.55	$112.60
Purchase #4	$150.82	11.681%	$168.4373	$168.44	$168.45	$168.40
Purchase #5	$78.47	6.801%	$83.8067	$83.81	$83.80	$83.80
Purchase #6	$79.56	10.757%	$88.1183	$88.12	$88.10	$88.10
Purchase #7	$203.51	7.127%	$218.0142	$218.01	$218.00	$218.00
7 purchase totals =	$854.09		$919.7546	$919.76	$919.70	$919.80