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	$38.71	6.476%	$41.2169	$41.22	$41.20	$41.20
Purchase #2	$28.38	9.334%	$31.029	$31.03	$31.05	$31.00
Purchase #3	$42.67	13.596%	$48.4714	$48.47	$48.45	$48.50
Purchase #4	$70.48	3.327%	$72.8249	$72.82	$72.80	$72.80
Purchase #5	$109.89	12.566%	$123.6988	$123.70	$123.70	$123.70
Purchase #6	$166.74	8.671%	$181.198	$181.20	$181.20	$181.20
Purchase #7	$127.95	8.569%	$138.914	$138.91	$138.90	$138.90
7 purchase totals =	$584.82		$637.3530	$637.35	$637.30	$637.30