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	$31.73	11.269%	$35.3057	$35.31	$35.30	$35.30
Purchase #2	$55.52	7.296%	$59.5707	$59.57	$59.55	$59.60
Purchase #3	$250.81	11.846%	$280.521	$280.52	$280.50	$280.50
Purchase #4	$182.88	9.449%	$200.1603	$200.16	$200.15	$200.20
Purchase #5	$227.92	6.862%	$243.5599	$243.56	$243.55	$243.60
Purchase #6	$241.56	8.627%	$262.3994	$262.40	$262.40	$262.40
Purchase #7	$121.52	9.271%	$132.7861	$132.79	$132.80	$132.80
7 purchase totals =	$1,111.94		$1,214.3031	$1,214.31	$1,214.25	$1,214.40