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	$124.85	12.508%	$140.4662	$140.47	$140.45	$140.50
Purchase #2	$91.58	5.130%	$96.2781	$96.28	$96.30	$96.30
Purchase #3	$216.36	11.183%	$240.5555	$240.56	$240.55	$240.60
Purchase #4	$216.88	5.255%	$228.277	$228.28	$228.30	$228.30
Purchase #5	$88.46	10.811%	$98.0234	$98.02	$98.00	$98.00
Purchase #6	$214.82	3.582%	$222.5149	$222.51	$222.50	$222.50
Purchase #7	$31.86	5.376%	$33.5728	$33.57	$33.55	$33.60
7 purchase totals =	$984.81		$1,059.6879	$1,059.69	$1,059.65	$1,059.80