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	$200.71	10.809%	$222.4047	$222.40	$222.40	$222.40
Purchase #2	$106.70	11.710%	$119.1946	$119.19	$119.20	$119.20
Purchase #3	$220.55	13.703%	$250.772	$250.77	$250.75	$250.80
Purchase #4	$51.46	10.387%	$56.8052	$56.81	$56.80	$56.80
Purchase #5	$42.81	11.750%	$47.8402	$47.84	$47.85	$47.80
Purchase #6	$34.53	9.728%	$37.8891	$37.89	$37.90	$37.90
Purchase #7	$221.46	7.834%	$238.8092	$238.81	$238.80	$238.80
7 purchase totals =	$878.22		$973.7150	$973.71	$973.70	$973.70