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	$52.77	9.324%	$57.6903	$57.69	$57.70	$57.70
Purchase #2	$161.62	12.119%	$181.2067	$181.21	$181.20	$181.20
Purchase #3	$101.73	9.659%	$111.5561	$111.56	$111.55	$111.60
Purchase #4	$165.78	4.789%	$173.7192	$173.72	$173.70	$173.70
Purchase #5	$195.46	13.643%	$222.1266	$222.13	$222.15	$222.10
Purchase #6	$201.81	13.661%	$229.3793	$229.38	$229.40	$229.40
Purchase #7	$200.98	6.189%	$213.4187	$213.42	$213.40	$213.40
7 purchase totals =	$1,080.15		$1,189.0969	$1,189.11	$1,189.10	$1,189.10