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	$49.84	10.856%	$55.2506	$55.25	$55.25	$55.30
Purchase #2	$219.84	5.123%	$231.1024	$231.10	$231.10	$231.10
Purchase #3	$152.59	6.783%	$162.9402	$162.94	$162.95	$162.90
Purchase #4	$131.63	8.624%	$142.9818	$142.98	$143.00	$143.00
Purchase #5	$140.33	8.739%	$152.5934	$152.59	$152.60	$152.60
Purchase #6	$81.65	6.485%	$86.945	$86.95	$86.95	$86.90
Purchase #7	$151.89	12.866%	$171.4322	$171.43	$171.45	$171.40
7 purchase totals =	$927.77		$1,003.2456	$1,003.24	$1,003.30	$1,003.20