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	$174.84	12.424%	$196.5621	$196.56	$196.55	$196.60
Purchase #2	$208.54	12.624%	$234.8661	$234.87	$234.85	$234.90
Purchase #3	$29.74	4.704%	$31.139	$31.14	$31.15	$31.10
Purchase #4	$193.40	3.487%	$200.1439	$200.14	$200.15	$200.10
Purchase #5	$6.51	7.264%	$6.9829	$6.98	$7.00	$7.00
Purchase #6	$17.87	3.825%	$18.5535	$18.55	$18.55	$18.60
Purchase #7	$57.60	8.760%	$62.6458	$62.65	$62.65	$62.60
7 purchase totals =	$688.50		$750.8933	$750.89	$750.90	$750.90