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	$9.89	9.189%	$10.7988	$10.80	$10.80	$10.80
Purchase #2	$99.34	4.706%	$104.0149	$104.01	$104.00	$104.00
Purchase #3	$215.99	12.672%	$243.3603	$243.36	$243.35	$243.40
Purchase #4	$156.64	6.418%	$166.6932	$166.69	$166.70	$166.70
Purchase #5	$87.90	5.155%	$92.4312	$92.43	$92.45	$92.40
Purchase #6	$104.95	10.817%	$116.3024	$116.30	$116.30	$116.30
Purchase #7	$91.62	5.749%	$96.8872	$96.89	$96.90	$96.90
7 purchase totals =	$766.33		$830.4880	$830.48	$830.50	$830.50