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	$39.84	6.182%	$42.3029	$42.30	$42.30	$42.30
Purchase #2	$56.87	5.291%	$59.879	$59.88	$59.90	$59.90
Purchase #3	$183.82	7.642%	$197.8675	$197.87	$197.85	$197.90
Purchase #4	$66.99	7.106%	$71.7503	$71.75	$71.75	$71.80
Purchase #5	$163.69	13.120%	$185.1661	$185.17	$185.15	$185.20
Purchase #6	$235.98	10.805%	$261.4776	$261.48	$261.50	$261.50
Purchase #7	$152.96	7.688%	$164.7196	$164.72	$164.70	$164.70
7 purchase totals =	$900.15		$983.1630	$983.17	$983.15	$983.30