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	$127.76	8.412%	$138.5072	$138.51	$138.50	$138.50
Purchase #2	$12.37	3.708%	$12.8287	$12.83	$12.85	$12.80
Purchase #3	$134.74	4.288%	$140.5177	$140.52	$140.50	$140.50
Purchase #4	$74.46	12.349%	$83.6551	$83.66	$83.65	$83.70
Purchase #5	$134.40	12.695%	$151.4621	$151.46	$151.45	$151.50
Purchase #6	$59.39	12.839%	$67.0151	$67.02	$67.00	$67.00
Purchase #7	$122.50	5.290%	$128.9803	$128.98	$129.00	$129.00
7 purchase totals =	$665.62		$722.9662	$722.98	$722.95	$723.00