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	$128.80	10.693%	$142.5726	$142.57	$142.55	$142.60
Purchase #2	$108.87	4.300%	$113.5514	$113.55	$113.55	$113.60
Purchase #3	$150.36	13.346%	$170.427	$170.43	$170.45	$170.40
Purchase #4	$169.60	11.161%	$188.5291	$188.53	$188.55	$188.50
Purchase #5	$151.75	11.296%	$168.8917	$168.89	$168.90	$168.90
Purchase #6	$219.83	10.404%	$242.7011	$242.70	$242.70	$242.70
Purchase #7	$170.84	10.745%	$189.1968	$189.20	$189.20	$189.20
7 purchase totals =	$1,100.05		$1,215.8697	$1,215.87	$1,215.90	$1,215.90