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	$6.74	4.294%	$7.0294	$7.03	$7.05	$7.00
Purchase #2	$177.73	10.586%	$196.5445	$196.54	$196.55	$196.50
Purchase #3	$25.29	10.499%	$27.9452	$27.95	$27.95	$27.90
Purchase #4	$64.30	3.582%	$66.6032	$66.60	$66.60	$66.60
Purchase #5	$245.59	13.636%	$279.0787	$279.08	$279.10	$279.10
Purchase #6	$93.55	6.542%	$99.67	$99.67	$99.65	$99.70
Purchase #7	$250.71	13.115%	$283.5906	$283.59	$283.60	$283.60
7 purchase totals =	$863.91		$960.4616	$960.46	$960.50	$960.40