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	$231.39	8.355%	$250.7226	$250.72	$250.70	$250.70
Purchase #2	$249.57	6.388%	$265.5125	$265.51	$265.50	$265.50
Purchase #3	$239.59	10.438%	$264.5984	$264.60	$264.60	$264.60
Purchase #4	$137.79	12.836%	$155.4767	$155.48	$155.50	$155.50
Purchase #5	$44.77	10.235%	$49.3522	$49.35	$49.35	$49.40
Purchase #6	$78.75	9.792%	$86.4612	$86.46	$86.45	$86.50
Purchase #7	$142.34	7.700%	$153.3002	$153.30	$153.30	$153.30
7 purchase totals =	$1,124.20		$1,225.4238	$1,225.42	$1,225.40	$1,225.50