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	$121.47	12.232%	$136.3282	$136.33	$136.35	$136.30
Purchase #2	$154.83	13.505%	$175.7398	$175.74	$175.75	$175.70
Purchase #3	$33.54	12.214%	$37.6366	$37.64	$37.65	$37.60
Purchase #4	$250.72	3.650%	$259.8713	$259.87	$259.85	$259.90
Purchase #5	$41.85	9.814%	$45.9572	$45.96	$45.95	$46.00
Purchase #6	$51.43	4.140%	$53.5592	$53.56	$53.55	$53.60
Purchase #7	$56.53	4.525%	$59.088	$59.09	$59.10	$59.10
7 purchase totals =	$710.37		$768.1803	$768.19	$768.20	$768.20