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	$102.89	12.218%	$115.4611	$115.46	$115.45	$115.50
Purchase #2	$78.81	13.707%	$89.6125	$89.61	$89.60	$89.60
Purchase #3	$133.41	7.608%	$143.5598	$143.56	$143.55	$143.60
Purchase #4	$213.33	9.292%	$233.1526	$233.15	$233.15	$233.20
Purchase #5	$39.94	4.376%	$41.6878	$41.69	$41.70	$41.70
Purchase #6	$113.58	10.741%	$125.7796	$125.78	$125.80	$125.80
Purchase #7	$135.78	7.785%	$146.3505	$146.35	$146.35	$146.40
7 purchase totals =	$817.74		$895.6039	$895.60	$895.60	$895.80