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	$84.67	5.337%	$89.1888	$89.19	$89.20	$89.20
Purchase #2	$196.52	5.280%	$206.8963	$206.90	$206.90	$206.90
Purchase #3	$144.99	13.663%	$164.8	$164.80	$164.80	$164.80
Purchase #4	$16.94	5.830%	$17.9276	$17.93	$17.95	$17.90
Purchase #5	$142.67	5.227%	$150.1274	$150.13	$150.15	$150.10
Purchase #6	$76.36	13.554%	$86.7098	$86.71	$86.70	$86.70
Purchase #7	$123.43	3.607%	$127.8821	$127.88	$127.90	$127.90
7 purchase totals =	$785.58		$843.5320	$843.54	$843.60	$843.50