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	$214.44	12.521%	$241.29	$241.29	$241.30	$241.30
Purchase #2	$85.70	12.320%	$96.2582	$96.26	$96.25	$96.30
Purchase #3	$174.55	12.380%	$196.1593	$196.16	$196.15	$196.20
Purchase #4	$236.98	4.692%	$248.0991	$248.10	$248.10	$248.10
Purchase #5	$211.90	12.706%	$238.824	$238.82	$238.80	$238.80
Purchase #6	$109.74	4.633%	$114.8243	$114.82	$114.80	$114.80
Purchase #7	$100.93	3.555%	$104.5181	$104.52	$104.50	$104.50
7 purchase totals =	$1,134.24		$1,239.9730	$1,239.97	$1,239.90	$1,240.00