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	$244.45	10.445%	$269.9828	$269.98	$270.00	$270.00
Purchase #2	$179.54	11.457%	$200.1099	$200.11	$200.10	$200.10
Purchase #3	$77.40	12.233%	$86.8683	$86.87	$86.85	$86.90
Purchase #4	$82.35	4.403%	$85.9759	$85.98	$86.00	$86.00
Purchase #5	$244.82	10.429%	$270.3523	$270.35	$270.35	$270.40
Purchase #6	$147.38	11.369%	$164.1356	$164.14	$164.15	$164.10
Purchase #7	$128.98	11.425%	$143.716	$143.72	$143.70	$143.70
7 purchase totals =	$1,104.92		$1,221.1408	$1,221.15	$1,221.15	$1,221.20