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	$176.38	13.179%	$199.6251	$199.63	$199.65	$199.60
Purchase #2	$200.73	12.540%	$225.9015	$225.90	$225.90	$225.90
Purchase #3	$43.29	9.102%	$47.2303	$47.23	$47.25	$47.20
Purchase #4	$46.70	8.225%	$50.5411	$50.54	$50.55	$50.50
Purchase #5	$96.40	7.777%	$103.897	$103.90	$103.90	$103.90
Purchase #6	$168.73	11.746%	$188.549	$188.55	$188.55	$188.50
Purchase #7	$131.95	6.380%	$140.3684	$140.37	$140.35	$140.40
7 purchase totals =	$864.18		$956.1124	$956.12	$956.15	$956.00