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	$107.38	12.538%	$120.8433	$120.84	$120.85	$120.80
Purchase #2	$28.80	8.857%	$31.3508	$31.35	$31.35	$31.40
Purchase #3	$56.93	3.801%	$59.0939	$59.09	$59.10	$59.10
Purchase #4	$53.41	11.481%	$59.542	$59.54	$59.55	$59.50
Purchase #5	$67.99	5.110%	$71.4643	$71.46	$71.45	$71.50
Purchase #6	$73.69	8.409%	$79.8866	$79.89	$79.90	$79.90
Purchase #7	$164.83	8.661%	$179.1059	$179.11	$179.10	$179.10
7 purchase totals =	$553.03		$601.2868	$601.28	$601.30	$601.30