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	$35.53	4.674%	$37.1907	$37.19	$37.20	$37.20
Purchase #2	$179.32	6.443%	$190.8736	$190.87	$190.85	$190.90
Purchase #3	$248.35	4.304%	$259.039	$259.04	$259.05	$259.00
Purchase #4	$187.67	13.660%	$213.3057	$213.31	$213.30	$213.30
Purchase #5	$124.50	13.201%	$140.9352	$140.94	$140.95	$140.90
Purchase #6	$79.38	3.870%	$82.452	$82.45	$82.45	$82.50
Purchase #7	$61.95	5.478%	$65.3436	$65.34	$65.35	$65.30
7 purchase totals =	$916.70		$989.1398	$989.14	$989.15	$989.10