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	$79.64	12.874%	$89.8929	$89.89	$89.90	$89.90
Purchase #2	$80.64	3.600%	$83.543	$83.54	$83.55	$83.50
Purchase #3	$207.73	5.329%	$218.7999	$218.80	$218.80	$218.80
Purchase #4	$196.55	5.148%	$206.6684	$206.67	$206.65	$206.70
Purchase #5	$118.40	7.694%	$127.5097	$127.51	$127.50	$127.50
Purchase #6	$240.94	8.682%	$261.8584	$261.86	$261.85	$261.90
Purchase #7	$27.32	10.311%	$30.137	$30.14	$30.15	$30.10
7 purchase totals =	$951.22		$1,018.4093	$1,018.41	$1,018.40	$1,018.40