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	$81.55	3.577%	$84.467	$84.47	$84.45	$84.50
Purchase #2	$92.64	10.349%	$102.2273	$102.23	$102.25	$102.20
Purchase #3	$51.42	5.463%	$54.2291	$54.23	$54.25	$54.20
Purchase #4	$226.43	13.408%	$256.7897	$256.79	$256.80	$256.80
Purchase #5	$86.34	11.799%	$96.5273	$96.53	$96.55	$96.50
Purchase #6	$237.30	5.491%	$250.3301	$250.33	$250.35	$250.30
Purchase #7	$156.73	11.327%	$174.4828	$174.48	$174.50	$174.50
7 purchase totals =	$932.41		$1,019.0533	$1,019.06	$1,019.15	$1,019.00