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	$28.49	12.476%	$32.0444	$32.04	$32.05	$32.00
Purchase #2	$40.82	5.355%	$43.0059	$43.01	$43.00	$43.00
Purchase #3	$215.75	13.806%	$245.5364	$245.54	$245.55	$245.50
Purchase #4	$72.92	12.303%	$81.8913	$81.89	$81.90	$81.90
Purchase #5	$134.36	10.208%	$148.0755	$148.08	$148.10	$148.10
Purchase #6	$72.85	8.120%	$78.7654	$78.77	$78.75	$78.80
Purchase #7	$184.74	7.777%	$199.1072	$199.11	$199.10	$199.10
7 purchase totals =	$749.93		$828.4261	$828.44	$828.45	$828.40