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	$79.78	13.612%	$90.6397	$90.64	$90.65	$90.60
Purchase #2	$83.47	13.678%	$94.887	$94.89	$94.90	$94.90
Purchase #3	$182.54	8.499%	$198.0541	$198.05	$198.05	$198.10
Purchase #4	$73.53	6.103%	$78.0175	$78.02	$78.00	$78.00
Purchase #5	$60.42	7.403%	$64.8929	$64.89	$64.90	$64.90
Purchase #6	$101.69	7.380%	$109.1947	$109.19	$109.20	$109.20
Purchase #7	$95.26	5.226%	$100.2383	$100.24	$100.25	$100.20
7 purchase totals =	$676.69		$735.9242	$735.92	$735.95	$735.90