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	$242.44	11.720%	$270.854	$270.85	$270.85	$270.90
Purchase #2	$144.36	12.574%	$162.5118	$162.51	$162.50	$162.50
Purchase #3	$71.53	13.288%	$81.0349	$81.03	$81.05	$81.00
Purchase #4	$216.85	12.659%	$244.301	$244.30	$244.30	$244.30
Purchase #5	$69.32	5.172%	$72.9052	$72.91	$72.90	$72.90
Purchase #6	$212.36	10.580%	$234.8277	$234.83	$234.85	$234.80
Purchase #7	$59.69	9.831%	$65.5581	$65.56	$65.55	$65.60
7 purchase totals =	$1,016.55		$1,131.9927	$1,131.99	$1,132.00	$1,132.00