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	$169.33	9.710%	$185.7719	$185.77	$185.75	$185.80
Purchase #2	$168.85	12.845%	$190.5388	$190.54	$190.55	$190.50
Purchase #3	$28.77	3.863%	$29.8814	$29.88	$29.90	$29.90
Purchase #4	$99.49	3.238%	$102.7115	$102.71	$102.70	$102.70
Purchase #5	$165.46	11.564%	$184.5938	$184.59	$184.60	$184.60
Purchase #6	$47.88	6.432%	$50.9596	$50.96	$50.95	$51.00
Purchase #7	$56.98	3.728%	$59.1042	$59.10	$59.10	$59.10
7 purchase totals =	$736.76		$803.5612	$803.55	$803.55	$803.60