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	$79.96	10.754%	$88.5589	$88.56	$88.55	$88.60
Purchase #2	$39.54	8.332%	$42.8345	$42.83	$42.85	$42.80
Purchase #3	$39.54	11.254%	$43.9898	$43.99	$44.00	$44.00
Purchase #4	$184.99	11.533%	$206.3249	$206.32	$206.30	$206.30
Purchase #5	$90.89	7.184%	$97.4195	$97.42	$97.40	$97.40
Purchase #6	$56.93	4.482%	$59.4816	$59.48	$59.50	$59.50
Purchase #7	$237.70	10.445%	$262.5278	$262.53	$262.55	$262.50
7 purchase totals =	$729.55		$801.1370	$801.13	$801.15	$801.10