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	$38.39	9.542%	$42.0532	$42.05	$42.05	$42.10
Purchase #2	$240.31	6.872%	$256.8241	$256.82	$256.80	$256.80
Purchase #3	$211.39	13.147%	$239.1814	$239.18	$239.20	$239.20
Purchase #4	$92.43	8.709%	$100.4797	$100.48	$100.50	$100.50
Purchase #5	$86.45	3.184%	$89.2026	$89.20	$89.20	$89.20
Purchase #6	$168.31	11.849%	$188.2531	$188.25	$188.25	$188.30
Purchase #7	$131.39	7.472%	$141.2075	$141.21	$141.20	$141.20
7 purchase totals =	$968.67		$1,057.2016	$1,057.19	$1,057.20	$1,057.30