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	$250.33	9.404%	$273.871	$273.87	$273.85	$273.90
Purchase #2	$204.42	9.550%	$223.9421	$223.94	$223.95	$223.90
Purchase #3	$119.55	3.338%	$123.5406	$123.54	$123.55	$123.50
Purchase #4	$93.68	10.119%	$103.1595	$103.16	$103.15	$103.20
Purchase #5	$99.60	13.712%	$113.2572	$113.26	$113.25	$113.30
Purchase #6	$196.25	11.451%	$218.7226	$218.72	$218.70	$218.70
Purchase #7	$52.97	9.374%	$57.9354	$57.94	$57.95	$57.90
7 purchase totals =	$1,016.80		$1,114.4284	$1,114.43	$1,114.40	$1,114.40