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	$19.64	8.276%	$21.2654	$21.27	$21.25	$21.30
Purchase #2	$156.78	11.380%	$174.6216	$174.62	$174.60	$174.60
Purchase #3	$250.79	12.482%	$282.0936	$282.09	$282.10	$282.10
Purchase #4	$147.51	11.272%	$164.1373	$164.14	$164.15	$164.10
Purchase #5	$114.29	8.596%	$124.1144	$124.11	$124.10	$124.10
Purchase #6	$126.95	5.553%	$133.9995	$134.00	$134.00	$134.00
Purchase #7	$99.30	10.438%	$109.6649	$109.66	$109.65	$109.70
7 purchase totals =	$915.26		$1,009.8967	$1,009.89	$1,009.85	$1,009.90