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	$11.88	11.206%	$13.2113	$13.21	$13.20	$13.20
Purchase #2	$196.98	10.809%	$218.2716	$218.27	$218.25	$218.30
Purchase #3	$38.46	7.829%	$41.471	$41.47	$41.45	$41.50
Purchase #4	$72.62	10.699%	$80.3896	$80.39	$80.40	$80.40
Purchase #5	$195.97	10.145%	$215.8512	$215.85	$215.85	$215.90
Purchase #6	$231.32	12.370%	$259.9343	$259.93	$259.95	$259.90
Purchase #7	$98.59	7.308%	$105.795	$105.80	$105.80	$105.80
7 purchase totals =	$845.82		$934.9240	$934.92	$934.90	$935.00