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	$78.33	13.748%	$89.0988	$89.10	$89.10	$89.10
Purchase #2	$179.40	6.730%	$191.4736	$191.47	$191.45	$191.50
Purchase #3	$32.29	5.274%	$33.993	$33.99	$34.00	$34.00
Purchase #4	$131.54	11.832%	$147.1038	$147.10	$147.10	$147.10
Purchase #5	$98.89	12.803%	$111.5509	$111.55	$111.55	$111.60
Purchase #6	$92.45	13.358%	$104.7995	$104.80	$104.80	$104.80
Purchase #7	$34.73	11.766%	$38.8163	$38.82	$38.80	$38.80
7 purchase totals =	$647.63		$716.8359	$716.83	$716.80	$716.90