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	$241.69	11.615%	$269.7623	$269.76	$269.75	$269.80
Purchase #2	$137.67	13.848%	$156.7345	$156.73	$156.75	$156.70
Purchase #3	$167.90	8.572%	$182.2924	$182.29	$182.30	$182.30
Purchase #4	$165.34	12.816%	$186.53	$186.53	$186.55	$186.50
Purchase #5	$237.25	7.730%	$255.5894	$255.59	$255.60	$255.60
Purchase #6	$28.97	12.491%	$32.5886	$32.59	$32.60	$32.60
Purchase #7	$141.39	10.541%	$156.2939	$156.29	$156.30	$156.30
7 purchase totals =	$1,120.21		$1,239.7911	$1,239.78	$1,239.85	$1,239.80