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	$128.53	12.118%	$144.1053	$144.11	$144.10	$144.10
Purchase #2	$33.77	3.757%	$35.0387	$35.04	$35.05	$35.00
Purchase #3	$241.33	3.527%	$249.8417	$249.84	$249.85	$249.80
Purchase #4	$187.85	4.630%	$196.5475	$196.55	$196.55	$196.50
Purchase #5	$233.32	3.870%	$242.3495	$242.35	$242.35	$242.30
Purchase #6	$37.25	4.404%	$38.8905	$38.89	$38.90	$38.90
Purchase #7	$20.99	13.315%	$23.7848	$23.78	$23.80	$23.80
7 purchase totals =	$883.04		$930.5580	$930.56	$930.60	$930.40