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	$48.65	12.712%	$54.8344	$54.83	$54.85	$54.80
Purchase #2	$247.58	4.456%	$258.6122	$258.61	$258.60	$258.60
Purchase #3	$231.90	10.166%	$255.475	$255.48	$255.50	$255.50
Purchase #4	$241.50	3.772%	$250.6094	$250.61	$250.60	$250.60
Purchase #5	$232.91	6.317%	$247.6229	$247.62	$247.60	$247.60
Purchase #6	$123.73	6.581%	$131.8727	$131.87	$131.85	$131.90
Purchase #7	$35.60	6.480%	$37.9069	$37.91	$37.90	$37.90
7 purchase totals =	$1,161.87		$1,236.9335	$1,236.93	$1,236.90	$1,236.90