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	$55.49	6.728%	$59.2234	$59.22	$59.20	$59.20
Purchase #2	$41.76	5.551%	$44.0781	$44.08	$44.10	$44.10
Purchase #3	$34.79	6.254%	$36.9658	$36.97	$36.95	$37.00
Purchase #4	$165.40	12.703%	$186.4108	$186.41	$186.40	$186.40
Purchase #5	$20.81	12.869%	$23.488	$23.49	$23.50	$23.50
Purchase #6	$142.85	5.403%	$150.5682	$150.57	$150.55	$150.60
Purchase #7	$79.25	13.836%	$90.215	$90.22	$90.20	$90.20
7 purchase totals =	$540.35		$590.9493	$590.96	$590.90	$591.00