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	$123.33	6.696%	$131.5882	$131.59	$131.60	$131.60
Purchase #2	$94.27	6.375%	$100.2797	$100.28	$100.30	$100.30
Purchase #3	$150.92	9.255%	$164.8876	$164.89	$164.90	$164.90
Purchase #4	$74.30	3.548%	$76.9362	$76.94	$76.95	$76.90
Purchase #5	$197.58	4.208%	$205.8942	$205.89	$205.90	$205.90
Purchase #6	$165.96	9.196%	$181.2217	$181.22	$181.20	$181.20
Purchase #7	$87.64	8.309%	$94.922	$94.92	$94.90	$94.90
7 purchase totals =	$894.00		$955.7296	$955.73	$955.75	$955.70