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	$210.78	3.189%	$217.5018	$217.50	$217.50	$217.50
Purchase #2	$159.48	9.695%	$174.9416	$174.94	$174.95	$174.90
Purchase #3	$246.62	13.230%	$279.2478	$279.25	$279.25	$279.20
Purchase #4	$98.78	12.328%	$110.9576	$110.96	$110.95	$111.00
Purchase #5	$235.64	12.725%	$265.6252	$265.63	$265.65	$265.60
Purchase #6	$80.37	11.711%	$89.7821	$89.78	$89.80	$89.80
Purchase #7	$241.43	13.310%	$273.5643	$273.56	$273.55	$273.60
7 purchase totals =	$1,273.10		$1,411.6204	$1,411.62	$1,411.65	$1,411.60