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	$115.78	11.682%	$129.3054	$129.31	$129.30	$129.30
Purchase #2	$221.46	6.709%	$236.3178	$236.32	$236.30	$236.30
Purchase #3	$105.48	4.131%	$109.8374	$109.84	$109.85	$109.80
Purchase #4	$68.77	10.195%	$75.7811	$75.78	$75.80	$75.80
Purchase #5	$127.82	5.272%	$134.5587	$134.56	$134.55	$134.60
Purchase #6	$97.48	3.385%	$100.7797	$100.78	$100.80	$100.80
Purchase #7	$77.90	5.368%	$82.0817	$82.08	$82.10	$82.10
7 purchase totals =	$814.69		$868.6618	$868.67	$868.70	$868.70