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	$164.65	9.311%	$179.9806	$179.98	$180.00	$180.00
Purchase #2	$157.35	8.831%	$171.2456	$171.25	$171.25	$171.20
Purchase #3	$159.30	12.318%	$178.9226	$178.92	$178.90	$178.90
Purchase #4	$28.83	10.594%	$31.8843	$31.88	$31.90	$31.90
Purchase #5	$112.46	10.179%	$123.9073	$123.91	$123.90	$123.90
Purchase #6	$246.27	13.798%	$280.2503	$280.25	$280.25	$280.30
Purchase #7	$119.51	5.374%	$125.9325	$125.93	$125.95	$125.90
7 purchase totals =	$988.37		$1,092.1232	$1,092.12	$1,092.15	$1,092.10