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	$76.99	7.213%	$82.5433	$82.54	$82.55	$82.50
Purchase #2	$194.31	3.768%	$201.6316	$201.63	$201.65	$201.60
Purchase #3	$115.38	9.509%	$126.3515	$126.35	$126.35	$126.40
Purchase #4	$236.59	11.837%	$264.5952	$264.60	$264.60	$264.60
Purchase #5	$77.69	10.502%	$85.849	$85.85	$85.85	$85.80
Purchase #6	$90.35	10.305%	$99.6606	$99.66	$99.65	$99.70
Purchase #7	$40.62	13.150%	$45.9615	$45.96	$45.95	$46.00
7 purchase totals =	$831.93		$906.5927	$906.59	$906.60	$906.60