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	$74.71	4.861%	$78.3417	$78.34	$78.35	$78.30
Purchase #2	$135.77	11.552%	$151.4542	$151.45	$151.45	$151.50
Purchase #3	$64.64	12.168%	$72.5054	$72.51	$72.50	$72.50
Purchase #4	$164.59	7.482%	$176.9046	$176.90	$176.90	$176.90
Purchase #5	$58.74	13.498%	$66.6687	$66.67	$66.65	$66.70
Purchase #6	$42.78	3.810%	$44.4099	$44.41	$44.40	$44.40
Purchase #7	$150.58	12.214%	$168.9718	$168.97	$168.95	$169.00
7 purchase totals =	$691.81		$759.2563	$759.25	$759.20	$759.30