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	$103.67	4.424%	$108.2564	$108.26	$108.25	$108.30
Purchase #2	$154.27	8.785%	$167.8226	$167.82	$167.80	$167.80
Purchase #3	$63.90	12.333%	$71.7808	$71.78	$71.80	$71.80
Purchase #4	$176.81	12.122%	$198.2429	$198.24	$198.25	$198.20
Purchase #5	$35.34	9.753%	$38.7867	$38.79	$38.80	$38.80
Purchase #6	$98.55	11.113%	$109.5019	$109.50	$109.50	$109.50
Purchase #7	$119.56	5.554%	$126.2004	$126.20	$126.20	$126.20
7 purchase totals =	$752.10		$820.5917	$820.59	$820.60	$820.60