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	$137.40	12.827%	$155.0243	$155.02	$155.00	$155.00
Purchase #2	$187.74	9.455%	$205.4908	$205.49	$205.50	$205.50
Purchase #3	$41.28	11.815%	$46.1572	$46.16	$46.15	$46.20
Purchase #4	$40.64	6.172%	$43.1483	$43.15	$43.15	$43.10
Purchase #5	$95.45	6.770%	$101.912	$101.91	$101.90	$101.90
Purchase #6	$90.92	9.409%	$99.4747	$99.47	$99.45	$99.50
Purchase #7	$186.47	7.199%	$199.894	$199.89	$199.90	$199.90
7 purchase totals =	$779.90		$851.1013	$851.09	$851.05	$851.10