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	$46.76	12.869%	$52.7775	$52.78	$52.80	$52.80
Purchase #2	$148.34	11.833%	$165.8931	$165.89	$165.90	$165.90
Purchase #3	$179.89	3.613%	$186.3894	$186.39	$186.40	$186.40
Purchase #4	$84.60	6.715%	$90.2809	$90.28	$90.30	$90.30
Purchase #5	$59.83	11.730%	$66.8481	$66.85	$66.85	$66.80
Purchase #6	$100.69	8.627%	$109.3765	$109.38	$109.40	$109.40
Purchase #7	$203.70	4.225%	$212.3063	$212.31	$212.30	$212.30
7 purchase totals =	$823.81		$883.8718	$883.88	$883.95	$883.90