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	$198.70	13.624%	$225.7709	$225.77	$225.75	$225.80
Purchase #2	$135.89	5.129%	$142.8598	$142.86	$142.85	$142.90
Purchase #3	$142.28	3.169%	$146.7889	$146.79	$146.80	$146.80
Purchase #4	$176.75	6.704%	$188.5993	$188.60	$188.60	$188.60
Purchase #5	$45.64	8.274%	$49.4163	$49.42	$49.40	$49.40
Purchase #6	$94.53	11.477%	$105.3792	$105.38	$105.40	$105.40
Purchase #7	$113.41	5.479%	$119.6237	$119.62	$119.60	$119.60
7 purchase totals =	$907.20		$978.4381	$978.44	$978.40	$978.50