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	$169.85	12.117%	$190.4307	$190.43	$190.45	$190.40
Purchase #2	$88.89	12.591%	$100.0821	$100.08	$100.10	$100.10
Purchase #3	$69.32	10.407%	$76.5341	$76.53	$76.55	$76.50
Purchase #4	$133.28	12.103%	$149.4109	$149.41	$149.40	$149.40
Purchase #5	$170.64	6.384%	$181.5337	$181.53	$181.55	$181.50
Purchase #6	$93.58	5.162%	$98.4106	$98.41	$98.40	$98.40
Purchase #7	$71.25	9.731%	$78.1833	$78.18	$78.20	$78.20
7 purchase totals =	$796.81		$874.5854	$874.57	$874.65	$874.50