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	$158.81	7.648%	$170.9558	$170.96	$170.95	$171.00
Purchase #2	$57.71	8.388%	$62.5507	$62.55	$62.55	$62.60
Purchase #3	$85.36	12.329%	$95.884	$95.88	$95.90	$95.90
Purchase #4	$94.65	9.779%	$103.9058	$103.91	$103.90	$103.90
Purchase #5	$93.36	7.581%	$100.4376	$100.44	$100.45	$100.40
Purchase #6	$133.37	9.142%	$145.5627	$145.56	$145.55	$145.60
Purchase #7	$97.98	6.671%	$104.5162	$104.52	$104.50	$104.50
7 purchase totals =	$721.24		$783.8128	$783.82	$783.80	$783.90