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	$17.81	13.288%	$20.1766	$20.18	$20.20	$20.20
Purchase #2	$12.76	13.347%	$14.4631	$14.46	$14.45	$14.50
Purchase #3	$142.56	6.280%	$151.5128	$151.51	$151.50	$151.50
Purchase #4	$112.48	10.816%	$124.6458	$124.65	$124.65	$124.60
Purchase #5	$196.89	6.330%	$209.3531	$209.35	$209.35	$209.40
Purchase #6	$83.49	3.717%	$86.5933	$86.59	$86.60	$86.60
Purchase #7	$187.60	12.656%	$211.3427	$211.34	$211.35	$211.30
7 purchase totals =	$753.59		$818.0874	$818.08	$818.10	$818.10