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	$137.87	13.147%	$155.9958	$156.00	$156.00	$156.00
Purchase #2	$189.54	3.398%	$195.9806	$195.98	$196.00	$196.00
Purchase #3	$74.54	12.508%	$83.8635	$83.86	$83.85	$83.90
Purchase #4	$124.45	12.485%	$139.9876	$139.99	$140.00	$140.00
Purchase #5	$196.86	13.641%	$223.7137	$223.71	$223.70	$223.70
Purchase #6	$160.83	11.536%	$179.3833	$179.38	$179.40	$179.40
Purchase #7	$80.97	7.496%	$87.0395	$87.04	$87.05	$87.00
7 purchase totals =	$965.06		$1,065.9640	$1,065.96	$1,066.00	$1,066.00