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	$37.86	4.319%	$39.4952	$39.50	$39.50	$39.50
Purchase #2	$141.95	3.322%	$146.6656	$146.67	$146.65	$146.70
Purchase #3	$128.41	10.150%	$141.4436	$141.44	$141.45	$141.40
Purchase #4	$42.40	12.180%	$47.5643	$47.56	$47.55	$47.60
Purchase #5	$245.92	4.457%	$256.8807	$256.88	$256.90	$256.90
Purchase #6	$103.39	12.225%	$116.0294	$116.03	$116.05	$116.00
Purchase #7	$173.72	7.818%	$187.3014	$187.30	$187.30	$187.30
7 purchase totals =	$873.65		$935.3802	$935.38	$935.40	$935.40