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	$6.83	3.804%	$7.0898	$7.09	$7.10	$7.10
Purchase #2	$177.47	13.192%	$200.8818	$200.88	$200.90	$200.90
Purchase #3	$54.62	12.318%	$61.3481	$61.35	$61.35	$61.30
Purchase #4	$224.81	11.340%	$250.3035	$250.30	$250.30	$250.30
Purchase #5	$43.94	12.272%	$49.3323	$49.33	$49.35	$49.30
Purchase #6	$94.98	3.777%	$98.5674	$98.57	$98.55	$98.60
Purchase #7	$230.78	10.737%	$255.5588	$255.56	$255.55	$255.60
7 purchase totals =	$833.43		$923.0817	$923.08	$923.10	$923.10