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	$79.48	3.270%	$82.079	$82.08	$82.10	$82.10
Purchase #2	$49.48	12.708%	$55.7679	$55.77	$55.75	$55.80
Purchase #3	$59.82	4.405%	$62.4551	$62.46	$62.45	$62.50
Purchase #4	$142.79	11.338%	$158.9795	$158.98	$159.00	$159.00
Purchase #5	$112.64	4.437%	$117.6378	$117.64	$117.65	$117.60
Purchase #6	$232.66	10.346%	$256.731	$256.73	$256.75	$256.70
Purchase #7	$156.54	7.453%	$168.2069	$168.21	$168.20	$168.20
7 purchase totals =	$833.41		$901.8572	$901.87	$901.90	$901.90