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	$46.99	8.480%	$50.9748	$50.97	$50.95	$51.00
Purchase #2	$24.89	3.793%	$25.8341	$25.83	$25.85	$25.80
Purchase #3	$203.32	6.489%	$216.5134	$216.51	$216.50	$216.50
Purchase #4	$123.32	3.506%	$127.6436	$127.64	$127.65	$127.60
Purchase #5	$164.81	10.788%	$182.5897	$182.59	$182.60	$182.60
Purchase #6	$33.60	4.190%	$35.0078	$35.01	$35.00	$35.00
Purchase #7	$100.38	3.701%	$104.0951	$104.10	$104.10	$104.10
7 purchase totals =	$697.31		$742.6585	$742.65	$742.65	$742.60