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	$18.91	7.513%	$20.3307	$20.33	$20.35	$20.30
Purchase #2	$84.29	11.615%	$94.0803	$94.08	$94.10	$94.10
Purchase #3	$172.48	5.864%	$182.5942	$182.59	$182.60	$182.60
Purchase #4	$58.55	12.108%	$65.6392	$65.64	$65.65	$65.60
Purchase #5	$225.61	12.785%	$254.4542	$254.45	$254.45	$254.50
Purchase #6	$194.63	7.688%	$209.5932	$209.59	$209.60	$209.60
Purchase #7	$123.33	11.504%	$137.5179	$137.52	$137.50	$137.50
7 purchase totals =	$877.80		$964.2097	$964.20	$964.25	$964.20