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	$128.56	8.166%	$139.0582	$139.06	$139.05	$139.10
Purchase #2	$65.39	6.209%	$69.4501	$69.45	$69.45	$69.50
Purchase #3	$51.47	7.124%	$55.1367	$55.14	$55.15	$55.10
Purchase #4	$236.55	8.240%	$256.0417	$256.04	$256.05	$256.00
Purchase #5	$163.30	9.564%	$178.918	$178.92	$178.90	$178.90
Purchase #6	$91.34	4.387%	$95.3471	$95.35	$95.35	$95.30
Purchase #7	$186.87	11.470%	$208.304	$208.30	$208.30	$208.30
7 purchase totals =	$923.48		$1,002.2558	$1,002.26	$1,002.25	$1,002.20