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	$160.42	12.778%	$180.9185	$180.92	$180.90	$180.90
Purchase #2	$165.85	6.537%	$176.6916	$176.69	$176.70	$176.70
Purchase #3	$160.40	13.112%	$181.4316	$181.43	$181.45	$181.40
Purchase #4	$119.28	9.732%	$130.8883	$130.89	$130.90	$130.90
Purchase #5	$89.34	9.517%	$97.8425	$97.84	$97.85	$97.80
Purchase #6	$99.87	5.731%	$105.5935	$105.59	$105.60	$105.60
Purchase #7	$38.45	4.612%	$40.2233	$40.22	$40.20	$40.20
7 purchase totals =	$833.61		$913.5893	$913.58	$913.60	$913.50