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	$125.78	3.761%	$130.5106	$130.51	$130.50	$130.50
Purchase #2	$14.77	5.656%	$15.6054	$15.61	$15.60	$15.60
Purchase #3	$232.77	3.235%	$240.3001	$240.30	$240.30	$240.30
Purchase #4	$143.63	5.377%	$151.353	$151.35	$151.35	$151.40
Purchase #5	$83.28	3.296%	$86.0249	$86.02	$86.00	$86.00
Purchase #6	$36.98	4.794%	$38.7528	$38.75	$38.75	$38.80
Purchase #7	$157.68	6.739%	$168.3061	$168.31	$168.30	$168.30
7 purchase totals =	$794.89		$830.8529	$830.85	$830.80	$830.90