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	$50.51	9.831%	$55.4756	$55.48	$55.50	$55.50
Purchase #2	$187.52	3.631%	$194.3289	$194.33	$194.35	$194.30
Purchase #3	$192.29	4.184%	$200.3354	$200.34	$200.35	$200.30
Purchase #4	$222.52	12.776%	$250.9492	$250.95	$250.95	$250.90
Purchase #5	$174.72	7.859%	$188.4512	$188.45	$188.45	$188.50
Purchase #6	$36.43	12.642%	$41.0355	$41.04	$41.05	$41.00
Purchase #7	$107.88	3.665%	$111.8338	$111.83	$111.85	$111.80
7 purchase totals =	$971.87		$1,042.4096	$1,042.42	$1,042.50	$1,042.30