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	$5.80	5.291%	$6.1069	$6.11	$6.10	$6.10
Purchase #2	$79.48	3.732%	$82.4462	$82.45	$82.45	$82.40
Purchase #3	$235.58	9.164%	$257.1686	$257.17	$257.15	$257.20
Purchase #4	$97.77	12.267%	$109.7634	$109.76	$109.75	$109.80
Purchase #5	$198.80	7.624%	$213.9565	$213.96	$213.95	$214.00
Purchase #6	$135.45	11.283%	$150.7328	$150.73	$150.75	$150.70
Purchase #7	$214.89	12.402%	$241.5407	$241.54	$241.55	$241.50
7 purchase totals =	$967.77		$1,061.7151	$1,061.72	$1,061.70	$1,061.70