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	$173.94	6.477%	$185.2061	$185.21	$185.20	$185.20
Purchase #2	$158.97	12.327%	$178.5662	$178.57	$178.55	$178.60
Purchase #3	$75.89	8.752%	$82.5319	$82.53	$82.55	$82.50
Purchase #4	$222.93	11.448%	$248.451	$248.45	$248.45	$248.50
Purchase #5	$196.88	6.444%	$209.5669	$209.57	$209.55	$209.60
Purchase #6	$88.98	7.690%	$95.8226	$95.82	$95.80	$95.80
Purchase #7	$194.97	13.437%	$221.1681	$221.17	$221.15	$221.20
7 purchase totals =	$1,112.56		$1,221.3128	$1,221.32	$1,221.25	$1,221.40