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	$113.90	12.712%	$128.379	$128.38	$128.40	$128.40
Purchase #2	$42.80	6.150%	$45.4322	$45.43	$45.45	$45.40
Purchase #3	$220.47	6.491%	$234.7807	$234.78	$234.80	$234.80
Purchase #4	$222.47	11.727%	$248.5591	$248.56	$248.55	$248.60
Purchase #5	$46.94	13.215%	$53.1431	$53.14	$53.15	$53.10
Purchase #6	$199.35	8.604%	$216.5021	$216.50	$216.50	$216.50
Purchase #7	$58.36	7.504%	$62.7393	$62.74	$62.75	$62.70
7 purchase totals =	$904.29		$989.5355	$989.53	$989.60	$989.50