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	$158.89	12.546%	$178.8243	$178.82	$178.80	$178.80
Purchase #2	$246.78	9.800%	$270.9644	$270.96	$270.95	$271.00
Purchase #3	$169.83	6.868%	$181.4939	$181.49	$181.50	$181.50
Purchase #4	$80.58	5.763%	$85.2238	$85.22	$85.20	$85.20
Purchase #5	$99.32	11.259%	$110.5024	$110.50	$110.50	$110.50
Purchase #6	$56.71	6.541%	$60.4194	$60.42	$60.40	$60.40
Purchase #7	$43.42	4.459%	$45.3561	$45.36	$45.35	$45.40
7 purchase totals =	$855.53		$932.7843	$932.77	$932.70	$932.80