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	$80.69	13.170%	$91.3169	$91.32	$91.30	$91.30
Purchase #2	$27.82	12.663%	$31.3428	$31.34	$31.35	$31.30
Purchase #3	$117.45	5.662%	$124.1	$124.10	$124.10	$124.10
Purchase #4	$176.89	7.571%	$190.2823	$190.28	$190.30	$190.30
Purchase #5	$237.61	13.293%	$269.1955	$269.20	$269.20	$269.20
Purchase #6	$211.78	4.297%	$220.8802	$220.88	$220.90	$220.90
Purchase #7	$27.89	11.477%	$31.0909	$31.09	$31.10	$31.10
7 purchase totals =	$880.13		$958.2086	$958.21	$958.25	$958.20