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	$155.41	12.868%	$175.4082	$175.41	$175.40	$175.40
Purchase #2	$246.61	3.861%	$256.1316	$256.13	$256.15	$256.10
Purchase #3	$73.31	4.162%	$76.3612	$76.36	$76.35	$76.40
Purchase #4	$69.51	13.526%	$78.9119	$78.91	$78.90	$78.90
Purchase #5	$200.61	7.602%	$215.8604	$215.86	$215.85	$215.90
Purchase #6	$140.25	3.550%	$145.2289	$145.23	$145.25	$145.20
Purchase #7	$171.94	11.463%	$191.6495	$191.65	$191.65	$191.60
7 purchase totals =	$1,057.64		$1,139.5517	$1,139.55	$1,139.55	$1,139.50