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	$78.90	4.858%	$82.733	$82.73	$82.75	$82.70
Purchase #2	$246.29	5.768%	$260.496	$260.50	$260.50	$260.50
Purchase #3	$224.73	7.351%	$241.2499	$241.25	$241.25	$241.20
Purchase #4	$128.98	10.258%	$142.2108	$142.21	$142.20	$142.20
Purchase #5	$144.60	7.563%	$155.5361	$155.54	$155.55	$155.50
Purchase #6	$101.69	11.404%	$113.2867	$113.29	$113.30	$113.30
Purchase #7	$77.35	11.474%	$86.2251	$86.23	$86.25	$86.20
7 purchase totals =	$1,002.54		$1,081.7376	$1,081.75	$1,081.80	$1,081.60