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	$140.64	6.576%	$149.8885	$149.89	$149.90	$149.90
Purchase #2	$123.77	6.429%	$131.7272	$131.73	$131.75	$131.70
Purchase #3	$138.84	5.859%	$146.9746	$146.97	$146.95	$147.00
Purchase #4	$238.33	12.639%	$268.4525	$268.45	$268.45	$268.50
Purchase #5	$71.32	8.160%	$77.1397	$77.14	$77.15	$77.10
Purchase #6	$134.33	4.565%	$140.4622	$140.46	$140.45	$140.50
Purchase #7	$54.72	11.503%	$61.0144	$61.01	$61.00	$61.00
7 purchase totals =	$901.95		$975.6591	$975.65	$975.65	$975.70