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	$29.76	5.529%	$31.4054	$31.41	$31.40	$31.40
Purchase #2	$200.93	7.299%	$215.5959	$215.60	$215.60	$215.60
Purchase #3	$136.65	3.288%	$141.1431	$141.14	$141.15	$141.10
Purchase #4	$200.37	7.832%	$216.063	$216.06	$216.05	$216.10
Purchase #5	$193.36	12.436%	$217.4062	$217.41	$217.40	$217.40
Purchase #6	$79.77	13.547%	$90.5764	$90.58	$90.60	$90.60
Purchase #7	$147.66	3.837%	$153.3257	$153.33	$153.35	$153.30
7 purchase totals =	$988.50		$1,065.5157	$1,065.53	$1,065.55	$1,065.50