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	$82.57	8.684%	$89.7404	$89.74	$89.75	$89.70
Purchase #2	$53.98	5.340%	$56.8625	$56.86	$56.85	$56.90
Purchase #3	$57.37	3.717%	$59.5024	$59.50	$59.50	$59.50
Purchase #4	$99.39	12.440%	$111.7541	$111.75	$111.75	$111.80
Purchase #5	$79.79	10.695%	$88.3235	$88.32	$88.30	$88.30
Purchase #6	$65.91	12.183%	$73.9398	$73.94	$73.95	$73.90
Purchase #7	$229.61	12.806%	$259.0139	$259.01	$259.00	$259.00
7 purchase totals =	$668.62		$739.1366	$739.12	$739.10	$739.10