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	$225.36	13.773%	$256.3988	$256.40	$256.40	$256.40
Purchase #2	$84.43	6.345%	$89.7871	$89.79	$89.80	$89.80
Purchase #3	$156.91	8.627%	$170.4466	$170.45	$170.45	$170.40
Purchase #4	$51.69	7.360%	$55.4944	$55.49	$55.50	$55.50
Purchase #5	$82.87	5.255%	$87.2248	$87.22	$87.20	$87.20
Purchase #6	$76.73	5.352%	$80.8366	$80.84	$80.85	$80.80
Purchase #7	$185.73	3.343%	$191.939	$191.94	$191.95	$191.90
7 purchase totals =	$863.72		$932.1273	$932.13	$932.15	$932.00