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	$25.84	5.747%	$27.325	$27.33	$27.35	$27.30
Purchase #2	$71.82	5.573%	$75.8225	$75.82	$75.80	$75.80
Purchase #3	$115.27	13.833%	$131.2153	$131.22	$131.20	$131.20
Purchase #4	$29.91	8.405%	$32.4239	$32.42	$32.40	$32.40
Purchase #5	$59.55	10.550%	$65.8325	$65.83	$65.85	$65.80
Purchase #6	$88.44	13.631%	$100.4953	$100.50	$100.50	$100.50
Purchase #7	$162.35	4.305%	$169.3392	$169.34	$169.35	$169.30
7 purchase totals =	$553.18		$602.4537	$602.46	$602.45	$602.30