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	$227.39	12.597%	$256.0343	$256.03	$256.05	$256.00
Purchase #2	$76.47	11.687%	$85.407	$85.41	$85.40	$85.40
Purchase #3	$79.26	10.115%	$87.2771	$87.28	$87.30	$87.30
Purchase #4	$208.48	4.851%	$218.5934	$218.59	$218.60	$218.60
Purchase #5	$105.28	10.294%	$116.1175	$116.12	$116.10	$116.10
Purchase #6	$198.83	12.838%	$224.3558	$224.36	$224.35	$224.40
Purchase #7	$39.95	6.182%	$42.4197	$42.42	$42.40	$42.40
7 purchase totals =	$935.66		$1,030.2048	$1,030.21	$1,030.20	$1,030.20