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	$179.71	6.651%	$191.6625	$191.66	$191.65	$191.70
Purchase #2	$172.62	10.659%	$191.0196	$191.02	$191.00	$191.00
Purchase #3	$195.60	8.122%	$211.4866	$211.49	$211.50	$211.50
Purchase #4	$81.57	7.737%	$87.8811	$87.88	$87.90	$87.90
Purchase #5	$199.60	12.459%	$224.4682	$224.47	$224.45	$224.50
Purchase #6	$24.72	12.832%	$27.8921	$27.89	$27.90	$27.90
Purchase #7	$54.42	9.212%	$59.4332	$59.43	$59.45	$59.40
7 purchase totals =	$908.24		$993.8433	$993.84	$993.85	$993.90