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	$76.80	4.801%	$80.4872	$80.49	$80.50	$80.50
Purchase #2	$65.27	4.113%	$67.9546	$67.95	$67.95	$68.00
Purchase #3	$103.47	6.259%	$109.9462	$109.95	$109.95	$109.90
Purchase #4	$82.30	7.344%	$88.3441	$88.34	$88.35	$88.30
Purchase #5	$32.78	3.291%	$33.8588	$33.86	$33.85	$33.90
Purchase #6	$7.83	9.319%	$8.5597	$8.56	$8.55	$8.60
Purchase #7	$159.62	12.299%	$179.2517	$179.25	$179.25	$179.30
7 purchase totals =	$528.07		$568.4023	$568.40	$568.40	$568.50