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	$40.90	3.758%	$42.437	$42.44	$42.45	$42.40
Purchase #2	$115.43	3.758%	$119.7679	$119.77	$119.75	$119.80
Purchase #3	$63.78	6.864%	$68.1579	$68.16	$68.15	$68.20
Purchase #4	$59.45	13.246%	$67.3247	$67.32	$67.30	$67.30
Purchase #5	$218.42	13.351%	$247.5813	$247.58	$247.60	$247.60
Purchase #6	$191.63	12.367%	$215.3289	$215.33	$215.35	$215.30
Purchase #7	$55.94	5.256%	$58.8802	$58.88	$58.90	$58.90
7 purchase totals =	$745.55		$819.4779	$819.48	$819.50	$819.50