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	$225.62	3.651%	$233.8574	$233.86	$233.85	$233.90
Purchase #2	$93.58	10.252%	$103.1738	$103.17	$103.15	$103.20
Purchase #3	$63.45	5.614%	$67.0121	$67.01	$67.00	$67.00
Purchase #4	$48.34	9.196%	$52.7853	$52.79	$52.80	$52.80
Purchase #5	$85.68	6.264%	$91.047	$91.05	$91.05	$91.00
Purchase #6	$81.29	9.839%	$89.2881	$89.29	$89.30	$89.30
Purchase #7	$172.41	5.424%	$181.7615	$181.76	$181.75	$181.80
7 purchase totals =	$770.37		$818.9252	$818.93	$818.90	$819.00