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	$228.61	12.147%	$256.3793	$256.38	$256.40	$256.40
Purchase #2	$119.44	10.486%	$131.9645	$131.96	$131.95	$132.00
Purchase #3	$59.34	3.740%	$61.5593	$61.56	$61.55	$61.60
Purchase #4	$86.35	6.159%	$91.6683	$91.67	$91.65	$91.70
Purchase #5	$209.47	5.570%	$221.1375	$221.14	$221.15	$221.10
Purchase #6	$133.92	5.152%	$140.8196	$140.82	$140.80	$140.80
Purchase #7	$90.45	13.507%	$102.6671	$102.67	$102.65	$102.70
7 purchase totals =	$927.58		$1,006.1956	$1,006.20	$1,006.15	$1,006.30