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	$240.83	5.868%	$254.9619	$254.96	$254.95	$255.00
Purchase #2	$104.51	4.767%	$109.492	$109.49	$109.50	$109.50
Purchase #3	$250.50	5.534%	$264.3627	$264.36	$264.35	$264.40
Purchase #4	$179.34	9.687%	$196.7127	$196.71	$196.70	$196.70
Purchase #5	$88.35	5.387%	$93.1094	$93.11	$93.10	$93.10
Purchase #6	$196.55	10.828%	$217.8324	$217.83	$217.85	$217.80
Purchase #7	$131.60	8.506%	$142.7939	$142.79	$142.80	$142.80
7 purchase totals =	$1,191.68		$1,279.2650	$1,279.25	$1,279.25	$1,279.30