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	$61.89	8.734%	$67.2955	$67.30	$67.30	$67.30
Purchase #2	$129.91	8.228%	$140.599	$140.60	$140.60	$140.60
Purchase #3	$28.55	11.804%	$31.92	$31.92	$31.90	$31.90
Purchase #4	$240.96	9.814%	$264.6078	$264.61	$264.60	$264.60
Purchase #5	$47.62	8.182%	$51.5163	$51.52	$51.50	$51.50
Purchase #6	$103.94	12.665%	$117.104	$117.10	$117.10	$117.10
Purchase #7	$247.96	10.853%	$274.8711	$274.87	$274.85	$274.90
7 purchase totals =	$860.83		$947.9137	$947.92	$947.85	$947.90