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	$159.25	3.479%	$164.7903	$164.79	$164.80	$164.80
Purchase #2	$201.31	8.234%	$217.8859	$217.89	$217.90	$217.90
Purchase #3	$116.94	3.265%	$120.7581	$120.76	$120.75	$120.80
Purchase #4	$21.48	12.415%	$24.1467	$24.15	$24.15	$24.10
Purchase #5	$102.57	13.551%	$116.4693	$116.47	$116.45	$116.50
Purchase #6	$31.76	10.428%	$35.0719	$35.07	$35.05	$35.10
Purchase #7	$96.73	3.206%	$99.8312	$99.83	$99.85	$99.80
7 purchase totals =	$730.04		$778.9534	$778.96	$778.95	$779.00