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	$119.85	9.273%	$130.9637	$130.96	$130.95	$131.00
Purchase #2	$119.87	3.845%	$124.479	$124.48	$124.50	$124.50
Purchase #3	$77.29	11.506%	$86.183	$86.18	$86.20	$86.20
Purchase #4	$98.38	7.446%	$105.7054	$105.71	$105.70	$105.70
Purchase #5	$92.34	4.546%	$96.5378	$96.54	$96.55	$96.50
Purchase #6	$38.34	5.576%	$40.4778	$40.48	$40.50	$40.50
Purchase #7	$14.83	6.859%	$15.8472	$15.85	$15.85	$15.80
7 purchase totals =	$560.90		$600.1939	$600.20	$600.25	$600.20