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	$52.65	9.150%	$57.4675	$57.47	$57.45	$57.50
Purchase #2	$5.46	10.790%	$6.0491	$6.05	$6.05	$6.00
Purchase #3	$202.36	10.638%	$223.8871	$223.89	$223.90	$223.90
Purchase #4	$74.83	13.763%	$85.1289	$85.13	$85.15	$85.10
Purchase #5	$70.99	10.651%	$78.5511	$78.55	$78.55	$78.60
Purchase #6	$108.65	11.771%	$121.4392	$121.44	$121.45	$121.40
Purchase #7	$91.67	9.358%	$100.2485	$100.25	$100.25	$100.20
7 purchase totals =	$606.61		$672.7714	$672.78	$672.80	$672.70