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	$229.47	13.748%	$261.0175	$261.02	$261.00	$261.00
Purchase #2	$138.67	10.223%	$152.8462	$152.85	$152.85	$152.80
Purchase #3	$249.75	8.211%	$270.257	$270.26	$270.25	$270.30
Purchase #4	$67.32	5.381%	$70.9425	$70.94	$70.95	$70.90
Purchase #5	$180.86	8.526%	$196.2801	$196.28	$196.30	$196.30
Purchase #6	$189.89	12.556%	$213.7326	$213.73	$213.75	$213.70
Purchase #7	$158.65	13.196%	$179.5855	$179.59	$179.60	$179.60
7 purchase totals =	$1,214.61		$1,344.6614	$1,344.67	$1,344.70	$1,344.60