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	$99.50	11.453%	$110.8957	$110.90	$110.90	$110.90
Purchase #2	$196.29	12.608%	$221.0382	$221.04	$221.05	$221.00
Purchase #3	$228.67	4.721%	$239.4655	$239.47	$239.45	$239.50
Purchase #4	$199.76	11.545%	$222.8223	$222.82	$222.80	$222.80
Purchase #5	$87.96	12.307%	$98.7852	$98.79	$98.80	$98.80
Purchase #6	$79.38	3.683%	$82.3036	$82.30	$82.30	$82.30
Purchase #7	$200.71	12.108%	$225.012	$225.01	$225.00	$225.00
7 purchase totals =	$1,092.27		$1,200.3225	$1,200.33	$1,200.30	$1,200.30