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	$7.65	11.417%	$8.5234	$8.52	$8.50	$8.50
Purchase #2	$247.78	3.226%	$255.7734	$255.77	$255.75	$255.80
Purchase #3	$102.82	12.712%	$115.8905	$115.89	$115.90	$115.90
Purchase #4	$81.29	10.534%	$89.8531	$89.85	$89.85	$89.90
Purchase #5	$222.97	12.814%	$251.5414	$251.54	$251.55	$251.50
Purchase #6	$45.25	10.416%	$49.9632	$49.96	$49.95	$50.00
Purchase #7	$211.64	9.445%	$231.6294	$231.63	$231.65	$231.60
7 purchase totals =	$919.40		$1,003.1744	$1,003.16	$1,003.15	$1,003.20