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	$88.98	4.329%	$92.8319	$92.83	$92.85	$92.80
Purchase #2	$112.61	6.814%	$120.2832	$120.28	$120.30	$120.30
Purchase #3	$250.78	11.818%	$280.4172	$280.42	$280.40	$280.40
Purchase #4	$151.46	10.268%	$167.0119	$167.01	$167.00	$167.00
Purchase #5	$59.67	9.224%	$65.174	$65.17	$65.15	$65.20
Purchase #6	$19.31	3.181%	$19.9243	$19.92	$19.90	$19.90
Purchase #7	$38.54	3.143%	$39.7513	$39.75	$39.75	$39.80
7 purchase totals =	$721.35		$785.3938	$785.38	$785.35	$785.40