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	$242.49	6.317%	$257.8081	$257.81	$257.80	$257.80
Purchase #2	$182.28	7.737%	$196.383	$196.38	$196.40	$196.40
Purchase #3	$132.37	11.106%	$147.071	$147.07	$147.05	$147.10
Purchase #4	$158.29	12.460%	$178.0129	$178.01	$178.00	$178.00
Purchase #5	$67.92	6.691%	$72.4645	$72.46	$72.45	$72.50
Purchase #6	$142.44	9.514%	$155.9917	$155.99	$156.00	$156.00
Purchase #7	$187.82	4.609%	$196.4766	$196.48	$196.50	$196.50
7 purchase totals =	$1,113.61		$1,204.2078	$1,204.20	$1,204.20	$1,204.30