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	$116.37	13.321%	$131.8716	$131.87	$131.85	$131.90
Purchase #2	$234.77	13.599%	$266.6964	$266.70	$266.70	$266.70
Purchase #3	$119.85	13.455%	$135.9758	$135.98	$136.00	$136.00
Purchase #4	$58.57	13.522%	$66.4898	$66.49	$66.50	$66.50
Purchase #5	$171.84	7.475%	$184.685	$184.69	$184.70	$184.70
Purchase #6	$159.91	13.456%	$181.4275	$181.43	$181.45	$181.40
Purchase #7	$92.36	7.678%	$99.4514	$99.45	$99.45	$99.50
7 purchase totals =	$953.67		$1,066.5975	$1,066.61	$1,066.65	$1,066.70