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	$80.87	7.424%	$86.8738	$86.87	$86.85	$86.90
Purchase #2	$79.34	5.295%	$83.5411	$83.54	$83.55	$83.50
Purchase #3	$78.43	3.144%	$80.8958	$80.90	$80.90	$80.90
Purchase #4	$38.46	8.851%	$41.8641	$41.86	$41.85	$41.90
Purchase #5	$177.83	10.567%	$196.6213	$196.62	$196.60	$196.60
Purchase #6	$205.38	12.656%	$231.3729	$231.37	$231.35	$231.40
Purchase #7	$197.96	3.358%	$204.6075	$204.61	$204.60	$204.60
7 purchase totals =	$858.27		$925.7765	$925.77	$925.70	$925.80