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	$57.72	3.440%	$59.7056	$59.71	$59.70	$59.70
Purchase #2	$155.61	8.831%	$169.3519	$169.35	$169.35	$169.40
Purchase #3	$64.50	11.646%	$72.0117	$72.01	$72.00	$72.00
Purchase #4	$225.49	5.848%	$238.6767	$238.68	$238.70	$238.70
Purchase #5	$143.25	9.467%	$156.8115	$156.81	$156.80	$156.80
Purchase #6	$31.98	3.564%	$33.1198	$33.12	$33.10	$33.10
Purchase #7	$170.96	6.224%	$181.6006	$181.60	$181.60	$181.60
7 purchase totals =	$849.51		$911.2778	$911.28	$911.25	$911.30