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	$50.85	11.629%	$56.7633	$56.76	$56.75	$56.80
Purchase #2	$159.64	12.645%	$179.8265	$179.83	$179.85	$179.80
Purchase #3	$163.39	6.770%	$174.4515	$174.45	$174.45	$174.50
Purchase #4	$248.71	13.516%	$282.3256	$282.33	$282.35	$282.30
Purchase #5	$115.72	6.635%	$123.398	$123.40	$123.40	$123.40
Purchase #6	$138.63	9.684%	$152.0549	$152.05	$152.05	$152.10
Purchase #7	$247.72	3.347%	$256.0112	$256.01	$256.00	$256.00
7 purchase totals =	$1,124.66		$1,224.8310	$1,224.83	$1,224.85	$1,224.90