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	$71.77	10.593%	$79.3726	$79.37	$79.35	$79.40
Purchase #2	$73.85	11.671%	$82.469	$82.47	$82.45	$82.50
Purchase #3	$156.62	6.844%	$167.3391	$167.34	$167.35	$167.30
Purchase #4	$12.36	8.568%	$13.419	$13.42	$13.40	$13.40
Purchase #5	$201.54	9.372%	$220.4283	$220.43	$220.45	$220.40
Purchase #6	$100.42	5.468%	$105.911	$105.91	$105.90	$105.90
Purchase #7	$91.81	13.672%	$104.3623	$104.36	$104.35	$104.40
7 purchase totals =	$708.37		$773.3013	$773.30	$773.25	$773.30