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	11.772%	$139.5473	$139.55	$139.55	$139.50
Purchase #2	$60.96	10.731%	$67.5016	$67.50	$67.50	$67.50
Purchase #3	$223.88	10.166%	$246.6396	$246.64	$246.65	$246.60
Purchase #4	$240.73	3.760%	$249.7814	$249.78	$249.80	$249.80
Purchase #5	$10.47	11.372%	$11.6606	$11.66	$11.65	$11.70
Purchase #6	$60.25	9.830%	$66.1726	$66.17	$66.15	$66.20
Purchase #7	$31.26	6.656%	$33.3407	$33.34	$33.35	$33.30
7 purchase totals =	$752.40		$814.6438	$814.64	$814.65	$814.60