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	$231.47	3.578%	$239.752	$239.75	$239.75	$239.80
Purchase #2	$53.52	3.721%	$55.5115	$55.51	$55.50	$55.50
Purchase #3	$131.95	11.673%	$147.3525	$147.35	$147.35	$147.40
Purchase #4	$80.82	12.163%	$90.6501	$90.65	$90.65	$90.70
Purchase #5	$33.84	4.552%	$35.3804	$35.38	$35.40	$35.40
Purchase #6	$182.41	3.700%	$189.1592	$189.16	$189.15	$189.20
Purchase #7	$176.78	13.599%	$200.8203	$200.82	$200.80	$200.80
7 purchase totals =	$890.79		$958.6260	$958.62	$958.60	$958.80